Photovoltaic device comprising a metal halide perovskite and a passivating agent

ABSTRACT

The present invention relates to devices comprising metal halide perovskites and organic passivating agents. In particular, the invention relates to photovoltaic and optoelectronic devices comprising passivated metal halide perovskites. The device according to the invention comprises: (a) a metal halide perovskite; and (b) a passivating agent which is an organic compound; wherein molecules of the passivating agent are chemically bonded to anions or cations in the metal halide perovskite. The invention also provides a process for producing a photovoltaic device, which photovoltaic device comprises: (a) a metal halide perovskite; and (b) a passivating agent which is an organic compound; wherein molecules of the passivating agent are chemically bonded to anions or cations in the metal halide perovskite, wherein the process comprises treating a metal halide perovskite with a passivating agent, which passivating agent is an organic compound and is suitable for chemically bonding to anions or cations in the metal halide perovskite.

FIELD OF THE INVENTION

The present invention relates to devices comprising metal halideperovskites and organic passivating agents. In particular, the inventionrelates to photovoltaic and optoelectronic devices comprising passivatedmetal halide perovskites.

BACKGROUND OF THE INVENTION

Photovoltaic (PV) cells, capable of converting sunlight directly intoelectricity, could ultimately be the solution to global energy demand.When the first crystalline silicon (c-Si) PV device was demonstrated in1954, the envisaged manufacturing costs made this technology impracticalfor large scale power generation. Thereafter, exploiting new materialsand fabrication procedures has attracted a growing effort to realizelower-cost photovoltaic technologies. In particular, the recentemergence of organometal-halide perovskite based solar cells promises todeliver one of the lowest cost technologies that is capable ofconverting sun light to electricity at the highest efficiencies.

In perovskites, as well as for most ionic crystals, the coordinationnumber for ions at the crystal surfaces is always lower than in the bulkmaterial. The consequent non-stoichiometric material comprises a localexcess of positive or negative ions, depending on the Miller index ofthe exposed surface. Such polar surfaces are known to be unstable, andtheir apparent natural occurrence has been associated with adsorption offoreign atoms, including oxygen and hydrogen from the moisture in air,which can passivate the crystal surface by balancing the local excesscharge. For the particular case of a crystal of a perovskite such asCH₃NH₃PbX₃ (where X is one or more halide anions), under-coordinatedmetal cations at the crystal surface would be unstable in air and canform lead oxide and hydroxide species when exposed to oxygen and waterfrom the air. Similarly, under-coordinated organic cations at thecrystal surface may bind with water molecules via hydrogen bridges,which causes hydration of the crystal surface. Conversely, halide anionsin crystalline materials have been reported to be relatively stable toair exposure (Abate, A. et al., Journal of Fluorine Chemistry 130,1171-1177 (2009)). Therefore, while it would be expected to find fewer“free” metal cations and organic cations when the devices are processedin air, it is likely that an excess of under-coordinated halide anionswould be present at the crystal surface.

In U.S. Pat. No. 7,491,642 organic passivating layers have beeninvestigated for silicon. The process described therein comprisescarrying out chemical reactions of the silicon surface with organicpassivating agents to produce passivating groups that are directlybonded to the surface by covalent (for instance Si—C) bonds.

As another example, as a means to control the growth of metalchalcogenide nanoparticles and ensure that they are well dispersed in asolvent of choice, coordinating ligands are employed (Ip A. et al.,Hybrid passivated colloidal quantum dot solids, Nature Nanotechnology,577, 7, (2012)). During the synthesis these ligands will typically belong alkane chain acid terminated molecules. These ligands make thenanocrystals highly soluble, advantageous for solution processing.However, since the ligands contain long insulating chains, they tend toprevent direct contact between the nanocrystals when processed into athin film. This is overcome by performing a ligand exchange, whereby asolid as deposited nanocrystal film is rinsed in a solution of adifferent double ended short-chain ligand. Through mass-action,predominant ligand exchange occurs with the long chain ligands beingreplaced by the smaller double ended ligands. The short-chain doubleended ligands enable closer proximity between the nanocrystals and canalso bind to two different nanocrystals at the same time,“cross-linking” the nanocrystals, making the film insoluble. In contrastto metal chalcogenide nanocrystals, the metal halide perovskitesdescribed herein are typically fabricated directly as continuous layersrather than collections of nanoparticles, and often comprise largecrystalline domains with domain sizes typically on the order of hundredsof nanometres to micrometers, much larger than the film thickness.Hence, there is no requirement to employ ligands in order to improve theinterconnection between perovskite crystals, as is required for metalchalcogenide nanocrystals.

In comparison to c-Si and other thin-film semiconductors, defect sitesand under-coordinated cations and anions in metal halide perovskitematerials have not thus far been considered deleterious to deviceperformance. However, the inventors have unexpectedly found thatelimination or passivation of defect sites and surface states in theperovskite material allows improved device efficiencies. It is thus anobject of the present invention to provide devices comprising passivatedmetal halide perovskites.

SUMMARY OF THE INVENTION

The inventors have found that significant recombination losses occurunder working conditions in perovskite devices due to charge trapping atthe perovskite/hole-transporter heterojunction. It has been identifiedthat under-coordinated cations and anions in the perovskite are at leastpartially responsible. In view of this, the inventors have established asupramolecular strategy for passivating the perovskite, includingpassivation of the perovskite surface. A range of passivating agentshave been investigated. The passivating agents are organic compoundswhich may (supramolecularly) chemically bond with anions or cations in,and/or at the surface of, the perovskite. By employing organicpassivating agents which chemically bond to anions or cations in theperovskite to produce passivated perovskite films, power conversionefficiencies (PCEs) of over 16% have been achieved for perovskitephotovoltaic devices, representing a step improvement for thetechnology. Organic passivating agents, for instance halogen bond donorcompounds and organic compounds comprising at least one thiol or sulfidegroup, have been shown to be particularly effective passivating agentsfor metal halide perovskites. Organic passivating agents comprising atleast one N atom have also been found to be effective passivating agentsfor metal halide perovskites.

In particular, the inventors have recognised that by using a passivatingagent which is an organic compound comprising cations that are largerthan the A cation in the ABX₃ perovskite crystal, and that are also toolarge to fit within the 3D perovskite structure, these cations willeffectively behave as impurities and may be expelled to the surfaces andgrain boundaries of the perovskite. Consequently, it has been found thatby employing impurity doping with a small concentration of largecations, it is possible to passivate both grain boundary defects andsurface defects. The organic passivating agent the effectively replacesthe A cation and interacts with the other ions in the perovskite thougha coulomb interaction. For example, when the metal halide perovskitecomprises a methyl ammonium (MA) cation, this could be achieved using apassivating agent which is an organic compound comprising any of butyl,pentyl. hexyl, phenyl-ethyl amines or phosphines.

In addition, the inventors have recognised that by using a passivatingagent which is an organic compound comprising cations with hydrophobicmoieties, these passivating agents may also act to “encapsulate” theperovskite crystals and inhibit moisture ingress. This can achievedintroducing the encapsulating passivating agent within the precursorsolution. By way of example, this could be achieved using a passivatingagent which is an organic compound such as an alkyl ammonium iodide, afluoroalky ammonium iodide etc. Alternatively, the perovskite can betreated with a passivating agent that enhances the moisture stabilityafter full crystallization. By way of example, this post treatment ofthe perovskite film could be implemented by immersion in a solution of apassivating agent which is an organic compound such as octyl ammonium,or octylammonium iodide.

Furthermore, the inventors have recognised that whilst some of thedefects will be present at the surfaces of the perovskite, there willalso be defect sites in bulk of the crystal structure of the perovskite.These defect sites in bulk of the crystal structure of the perovskitecan also be passivated using a passivating agent which is an organiccompound that chemically bonds with anions or cations at the defectsites. However, the inventors have also recognised that, at the planardefects formed by the grain boundaries within the perovskite, there willbe a strong coulomb interaction between the ions in the adjacent grains,which could induce further defect sites within the perovskite material.The inventors have therefore established a further strategy forpassivating grain boundary defect sites in bulk of the crystal structureof the perovskite.

In this further strategy, the passivating agents are organic compoundswhich are disposed at grain boundaries within the metal halideperovskite and that do not chemically bond to anions or cations in themetal halide perovskite. Preferably, such organic passivating agentscomprise non-polar organic molecules, such as polycyclic aromatichydrocarbons. In particular, the inventors have found that by addingnon-polar organic molecules to a solution of the metal halide perovskitebefore formation of the metal halide perovskite solid, where the organicmolecules do not specifically chemically bond to the perovskite,enhanced photoluminescence of the can be achieved. It is postulated thatthe organic molecules are expelled from the perovskite crystal grainsduring crystallisation and accumulate at the grain boundaries. Theorganic molecules within/at the grain boundaries then act toblock/inhibit coulomb interaction between anions and cations in adjacentgrains of the metal halide perovskite, thereby reducing the defectdensity.

Once passivated with passivating agents as described herein, thestability of perovskite films to ambient conditions is surprisinglygreatly enhanced. For instance, films of some perovskites (such asCH₃NH₃SnI₃ for example) are extremely sensitive to humidity in the air,and oxygen, and rapidly degrade turning colourless within seconds ofexposure to ambient conditions. However, the inventors have found thatthey may be made stable for hours, days and even weeks in ambientconditions following molecular passivation as described herein. Thus,perovskites such as CH₃NH₃SnI₃ which were known previously to be veryunstable, may now be stabilised over long periods, allowing their use indevices.

The inventors have introduced a passivation method for metal halideperovskite devices, by employing passivating agents, for instancehalogen bond donors (e.g. iodopentafluorobenzene) and organic moleculescomprising sulfur atoms (e.g. thiophene), in a supramolecular assembly.Passivating agents comprising nitrogen atoms (e.g. pyridine) may also beused as passivating agents in a supramolecular assembly. The PCE of thetreated solar cells can show increases of several percentage points(e.g. from 13% to over 16%), and the mechanism responsible for theenhancements has been elucidated: without treatment, under-coordinatedhalide anions and defect sites act as hole-traps leading to asignificant accumulation of charge at the perovskite/hole transporterheterojunction and within perovskite. This leads to faster recombinationand is likely to result in a disadvantageous charge density profilewithin the hole transporter and perovskite film, which should inhibitfast and efficient charge extraction under working conditions. Thepassivating agents can bind to and screen the electrostatic charge fromthe under-coordinated halide ions and defect sites, resolving the issue.Beyond advancing the current technology, this work demonstrates thatchemical treatments of the perovskite crystal can lead to enhancedoperation in the solar cells. Further improvements in both performanceand reproducibility are expected by pacifying any under-coordinatedcations (A, B and X ions) and defect sites, without relying onatmospheric oxygen and water. In addition, passivating agents canstabilize and protect perovskites which are typically unstable in air,such as tin and germanium based perovskites.

The inventors have thus developed efficient devices comprisingperovskites passivated with an organic passivating agent. According to afirst aspect, the invention provides a device comprising asemiconductor, which semiconductor comprises:

-   -   (a) a metal halide perovskite; and    -   (b) a passivating agent which is an organic compound;        wherein molecules of the passivating agent are chemically bonded        to anions or cations in the metal halide perovskite. The device        may be an optoelectronic device, for instance a photovoltaic        device.

The invention may also be applied to crystalline ionic solids ingeneral. Thus, the invention also provides a device comprising asemiconductor, which semiconductor comprises:

-   -   (a) a crystalline ionic solid; and    -   (b) a passivating agent which is an organic compound;        wherein molecules of the passivating agent are chemically bonded        to anions or cations in the crystalline ionic solid. The device        may be an optoelectronic device, for instance a photovoltaic        device.

The invention also provides a device comprising a semiconductor, whichsemiconductor comprises:

-   -   (a) a metal halide perovskite; and    -   (b) a passivating agent which is        -   (i) a halogen bond donor compound, or        -   (ii) an organic compound comprising at least one thiol or            sulfide group.

The device may be an optoelectronic device, for instance a photovoltaicdevice.

The invention also provides a process for producing a device comprisinga semiconductor, which semiconductor comprises:

-   -   (a) a metal halide perovskite; and    -   (b) a passivating agent which is an organic compound;    -   wherein molecules of the passivating agent are chemically bonded        to anions or cations in the metal halide perovskite,    -   wherein the process comprises treating a metal halide perovskite        with a passivating agent, which passivating agent is an organic        compound and is suitable for chemically bonding to anions or        cations in the metal halide perovskite.

The invention also provides a process for producing a device comprisinga semiconductor, which semiconductor comprises:

-   -   (a) a crystalline ionic solid; and    -   (b) a passivating agent which is an organic compound;    -   wherein molecules of the passivating agent are chemically bonded        to anions or cations in the crystalline ionic solid,    -   wherein the process comprises treating a crystalline ionic solid        with a passivating agent, which passivating agent is an organic        compound and is suitable for chemically bonding to anions or        cations in the crystalline ionic solid.

The device produced may be an optoelectronic device, for instance aphotovoltaic device.

The invention also provides a device obtainable by a process forproducing a device according to the invention. The device may be anoptoelectronic device, for instance a photovoltaic device.

In addition, according to a second aspect the invention provides adevice comprising a semiconductor, which semiconductor comprises:

-   -   (a) a metal halide perovskite; and    -   (b) a passivating agent which is an organic compound;        wherein molecules of the passivating agent are disposed at grain        boundaries within the metal halide perovskite and are not        chemically bonded to anions or cations in the metal halide        perovskite. The device may be an optoelectronic device, for        instance a photovoltaic device.

The invention therefore also provides a device comprising asemiconductor, which semiconductor comprises:

-   -   (a) a metal halide perovskite; and    -   (b) a passivating agent which is an organic compound comprising        non-polar organic molecules. The device may be an optoelectronic        device, for instance a photovoltaic device.

The invention also provides a process for producing a device comprisinga semiconductor, which semiconductor comprises:

-   -   (a) a metal halide perovskite; and    -   (b) a passivating agent which is an organic compound;    -   wherein molecules of the passivating agent are disposed at grain        boundaries within the metal halide perovskite and are not        chemically bonded to anions or cations in the metal halide        perovskite;    -   wherein the process comprises treating a metal halide perovskite        with a passivating agent, which passivating agent is an organic        compound that does not chemically bond to anions or cations in        the metal halide perovskite.

The device produced may be an optoelectronic device, for instance aphotovoltaic device. The invention also provides a device obtainable bya process for producing a device according to the invention. The devicemay be an optoelectronic device, for instance a photovoltaic device.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows: (a) Cross-sectional scanning electron microscopy of acomplete MSSC (meso super-structured solar cell); (b) Powder X-raydiffraction pattern (h 0 0, h=1-4) and crystal structure ofCH₃NH₃PbI_(3-x)Cl_(x) film on a glass substrate and its crystal unitcell (Pb, small spheres; X, large spheres, CH₃NH₃ ⁺ not shown); (c)Schematic view of the halogen bond interaction between theiodopentafluorobenzene (IPFB, halogen bond donor) and a generic halogenanion (X⁻=I⁻, Br⁻, Cl⁻, halogen bond acceptor) with sp³ hybridizedvalence electrons; (d) Proposed scenario for the IPFB assembly on thecrystal surface; (e)-(f) Solid-state ¹³C and ¹⁹F NMR spectra for IPFB asa pure liquid and when adsorbed onto the crystal surface. Inset FIG.1(e) zoom in at 120 ppm.

FIG. 2 shows: (a) JV curves and performance parameters (table inset) ofthe best perovskite MSSCs, with and without the IPFB treatment, usingSpiro-OMeTAD as hole transporter; devices were measured under AM1.5simulated sun light of 100 mW cm⁻² equivalent solar irradiance usingshadow masking to define the active area; (b) Distribution of the powerconversion efficiency (PCE) for more than 20 devices preparedsimultaneously; this experiment was repeated 4 times; (c) Illustrationof the CH₃NH₃PbX₃ crystals grown on a scaffold of Al₂O₃ nanoparticleswith IPFB present. (d) Light absorption of the perovskite films, withand without IPFB treatment (no Spiro-OMeTAD present).

FIG. 3 shows: (a) Ultrafast transient absorption spectra and dynamics at1100 nm of perovskite grown on a scaffold of Al₂O₃ nanoparticles (asdescribed in FIG. 2c ) and coated with Spiro-OMeTAD, with and withoutthe IPFB treatment; excitation at 500 nm (14 μJ/cm2); (b) Time resolvedphotoluminescence quenching, probing the emission from samples with andwithout Spiro-OMeTAD, with excitation at 510 nm; (c) Nanosecondtransient absorption dynamics for the IPFB treated (circles) anduntreated (squares) samples; excitation at 500 nm (100 μJ/cm2), probe at640 nm. The continuous lines represent the double-exponential fittingwith the shorter lifetimes (τ1) reported.

FIG. 4 shows: Photocurrent and photovoltage decay measurements for IPFBtreated and untreated perovskite-sensitized solar cells (PSSCs), asextracted from eight separate devices: (a) Recombination lifetimes(τ_(rec)) against the relative position of the electron quasi-Fermilevel with respect to the conduction band edge in the TiO₂(V_(cbe)−V_(F)); (b) Illustration of the electrostatic interactionbetween the under-coordinated halide (X⁻) on the perovskite surface andthe hole injected in the Spiro-OMeTAD; (c) Charge density at shortcircuit (ρ_(sc)) against short circuit photocurrent (Jsc); (d)Illustration of the electrostatic screening of the halide via halogenbond complexation of IPFB on the perovskite surface.

FIG. 5 shows a picture of films fabricated using the Sn based perovskiteCH₃NH₃SnI₃, coated upon fluorine doped tin oxide (FTO) coated glass,coated with both a compact and mesoporous layer of TiO₂ prior toperovskite coating. Here we see that the films which have beenpassivated using IPFB remain stable after being coated with a holetransporter, whereas the films without IPFB have undergone a significantdegree of degradation after a period of 24 hrs. With increasing Sncontent (indicated by percentage), the extent of film degradation ismore severe. IPFB passivation stabilises the film and slows down thedegradation process. (Films are coated with Spiro-OMeTAD.)

FIG. 6 shows the spread of performances for MSSCs employingCH₃NH₃PbI_(3-x)Cl_(x) as the absorber obtained for three differentsurface treatments as compared to a control device without any surfacetreatments. All devices were completely processed within an N₂ filledglovebox, and with a sample size of 16 individual devices for eachvariable investigated: iodopentafluorobenzene (IPFB),tetrahydrothiophene (THTh), thiophene (Th) and control devices. We seehere that for the passivated devices there is an improvement in deviceparameters when compared to the control.

FIG. 7 shows the J-V characteristics of the best performing devices forsurface treatment investigated: iodopentafluorobenzene (IPFB),tetrahydrothiophene (THTh), thiophene (Th) and a control device with nosurface treatments; as well as a table showing the maximum values of allthe device parameters.

FIG. 8 shows time resolved photoluminescence of the organolead mixedhalide perovskite CH₃NH₃PbI_(3-x)Cl_(x), with various passivationtreatments.

FIG. 9 shows steady state photoluminescence of the organolead mixedhalide perovskite CH₃NH₃PbI_(3-x)Cl_(x), with various passivationtreatments.

FIG. 10 shows the absorbance of a film of methylammonium triiodostannate(CH₃NH₃SnI₃) passivated with thiophene, after being stored in ambientindoor conditions (on the desk top in an office) for 3 weeks.

FIG. 11 shows device performance variations for devices prepared withand without IPFB treatment, where the thickness of a mesoporousdielectric scaffold is varied.

FIG. 12 shows device performance variations of devices prepared withdifferent iodoperfluorocarbons.

FIG. 13 shows device performance parameters for perovskite sensitizedsolar cells (PSSCs) comprising a 1.5 μm thick layer of mesoporous TiO₂,with and without IPFB treatment.

FIG. 14 shows photovoltage and photocurrent decay measurements for dyesensitized solar cells (DSSCs), prepared with and without IPFBtreatment.

FIG. 15 shows steady-state photoluminescence (PL) and photoluminescencequantum efficiency (PLQE) of passivated and unpassivated perovskitefilms.

FIG. 16 shows time-resolved PL of passivated and unpassivated perovskitefilms.

FIG. 17 shows current-voltage characteristics of pyridine-passivateddevice exhibiting hysteresis in current-voltage curves.

FIG. 18 shows performance parameters of a batch of passivated andunpassivated solar cells under simulated full sunlight.

FIG. 19 shows device results and stabilised maximum power for sensitisedand control devices.

FIG. 20 shows photoluminescence characteristics of neat, thiophene andpyridine passivated CH₃NH₃PbI_(3-x)Cl_(x) films: (a) time-resolvedphotoluminescence of thiophene and pyridine passivated perovskite filmsas compared to unpassivated films following a 507-nm pulsed excitation(200 kHz, 30nJ/cm²/pulse) (PL decays were acquired at the peak emissionwavelength (780 nm)); and (b) photoluminescence quantum efficiency(PLQE) of unpassivated films and films treated with thiophene andpyridine as a function of 532 CW laser excitation intensity.

FIG. 21 shows photoluminescence characteristics of bare and thiophene orpyridine passivated films. Time-resolved PL measurements of control,thiophene and pyridine samples with 507-nm pulsed (200 kHz) excitationat a range of pulse fluences corresponding to the quoted photoexcitationdensities. Solid lines are fits to the data using a model allowingextraction of the quoted trap densities N_(T).

FIG. 22: shows photoluminescence characteristics of octylamine (OA)doped CH₃NH₃PbI₃ perovskite films: (a) normalised steady-statephotoluminescence of OA doped perovskite films; (b) normalisedsteady-state photoluminescence of OA doped perovskite films.

FIG. 23: shows photoluminescence characteristics of octyl-ammoniumiodide (OAI) doped CH₃NH₃PbI₃ perovskite film. Time resolved PL decay of5 mol % OAI doped MAPbI3 perovskite film, where the actual compositionof the film is approximately [(0.95MA)(0.05OA)PbI3].

DETAILED DESCRIPTION OF THE INVENTION Definitions

The term “perovskite”, as used herein, refers to a material with athree-dimensional crystal structure related to that of CaTiO₃ or amaterial comprising a layer of material, which layer has a structurerelated to that of CaTiO₃. The structure of CaTiO₃ can be represented bythe formula ABX₃, wherein A and B are cations of different sizes and Xis an anion. In the unit cell, the A cations are at (0,0,0), the Bcations are at (½, ½, ½) and the X anions are at (½, ½, 0). The A cationis usually larger than the B cation. The skilled person will appreciatethat when A, B and X are varied, the different ion sizes may cause thestructure of the perovskite material to distort away from the structureadopted by CaTiO₃ to a lower-symmetry distorted structure. The symmetrywill also be lower if the material comprises a layer that has astructure related to that of CaTiO₃. Materials comprising a layer ofperovskite material are well known. For instance, the structure ofmaterials adopting the K₂NiF₄-type structure comprises a layer ofperovskite material. The skilled person will appreciate that aperovskite material can be represented by the formula [A][B][X]₃,wherein [A] is at least one cation, [B] is at least one cation and [X]is at least one anion. When the perovskite comprise more than one Acation, the different A cations may distributed over the A sites in anordered or disordered way. When the perovskite comprises more than one Bcation, the different B cations may distributed over the B sites in anordered or disordered way. When the perovskite comprise more than one Xanion, the different X anions may distributed over the X sites in anordered or disordered way. The symmetry of a perovskite comprising morethan one A cation, more than one B cation or more than one X cation,will be lower than that of CaTiO₃.

The term “metal halide perovskite”, as used herein, refers to aperovskite, the formula of which contains at least one metal cation andat least one halide anion. The term “organometal halide perovskite”, asused herein, refers to a metal halide perovskite, the formula of whichcontains at least one organic cation.

The term “crystalline ionic solid”, as used herein, refers to a solidwhich comprises a crystal structure comprising anions and cations, forinstance metal halide perovskites and organometal halide perovskites.The anions or cations may be any anions or cations. As the skilledperson will appreciate, crystal structures may have a degree of covalentbonding, however the term “crystalline ionic solid” still encompassescrystalline compounds having a degree of covalent bonding. Thus,compounds such as titanium dioxide and copper (I) iodide fall within theterm “crystalline ionic solid”.

The term “chemical bond”, as used herein, refers to an attractiveinteraction between two atoms or ions (including atom-atom, atom-ion andion-ion interactions). This may be a specific orbital interaction.“Chemical bond” includes supramolecular chemical bonds. The term“supramolecular chemical bond” as used herein means a chemical bond,wherein one atom or ion in the chemical bond is in one molecule and theother atom or ion is in a separate molecule or crystal structure, or isan isolated atom or ion. Supramolecular bonds are typically non-covalentbonds.

The term “chemically bonded”, as used herein, refers to two speciesselected from molecules, atoms or ions between which there is a chemicalbond, and includes reference to two species selected from molecules,atoms or ions bonded by a supramolecular chemical bond.

The term “halogen bond”, as used herein, refers to a non-covalentsupramolecular chemical bond formed between a halogen atom and a Lewisbase. In a halogen bond, the halogen atom acts as an electrophilicspecies which interacts with the nucleophilic Lewis base. Halogen atomsin organic molecules can be electron deficient due to electronwithdrawing effects of other moieties in the molecule, or due to theformation of induced dipoles. Lewis bases such as anions (includinghalide anions, in particular iodide) can interact strongly withhalogenated organic compounds via this specific supramolecularinteraction. This interaction defines any supramolecular non-covalentbond which involves a halogen atom as an electrophile. One of thestrongest reported halogen bond donors is iodopentafluorobenzene (IPFB,FIG. 1c ). In this compound, the highly electronegative fluorine atomsinductively withdraw electron density out of the aromatic ring, which inturn withdraws electron density from the iodine bonded to the aromaticring, leaving a partial positive charge on this halogen. Furthermore,the charge density on the iodine in IPFB is anisotropically distributed,with positive electrostatic potential localized opposite the carbon onthe extension of the C—I bond axis. This electropositive region caninteract attractively with any electron rich sites (for instance Lewisbases), and the interaction is especially strong with other halogenanions (X⁻, Lewis base, FIG. 1c ). Since this positive region on theiodine is surrounded by a belt of negative electrostatic potential, anyshift from a co-axial arrangement of —C—I . . . X⁻ (see FIG. 1c )results in electrostatic repulsions. Thus, the angle —C—I . . . X⁻ isalways close to 1800, whereas the I . . . X⁻ distance depends on theparticular crystalline structure.

The term “halogen bond donor compound”, as used herein, refers to acompound comprising an electrophilic halogen atom which may interactwith a Lewis base to form a halogen bond.

The term “chalcogen”, as used herein, refers to an element selected fromGroup 16 of the Periodic Table of the Elements. Thus, the chalcogensinclude O, S, Se, and Te. Occasionally, the chalcogens are not taken toinclude O. Thus, the chalcogens may be understood to include S, Se andTe.

The term “chalcogen-metal bond”, as used herein, refers to a chemicalbond formed between a chalcogen atom or anion and a metal atom orcation. This includes a chemical bond between an oxygen atom and a metalcation or atom, or a sulfur atom and a metal cation or atom.Chalcogen-metal bonds are often dative covalent bonds where the metalatom or cation acts as a Lewis acid and the chalcogen atom or anion actsas a Lewis base. Sulfur can form strong sulfur-metal bonds.

The term “under-coordinated”, as used herein, refers to an anion or acation in a crystal structure, the coordination of which is lower thanfor other ions of the same type in the rest (or bulk) of the crystal.For instance, if cations in the bulk of a crystal are coordinated by 6nearest neighbour anions, a cation in the same crystal structure whichis coordinated by 5 or fewer nearest neighbour anions is thereforeunder-coordinated. Under-coordinated ions may occur at the surface of acrystal due to no further unit cells of the crystal existing beyond thesurface to coordinate the ions at the surface, or under-coordinated ionsmay occur in the bulk of the crystal at sites where there a crystaldefect (i.e. defect sites), for instance a vacancy (i.e. an absence ofan ion, sometimes known as a Schottky defect, particularly when a pairof ions are absent), as ions adjacent to the vacancy will thus belacking one nearest neighbour counterion.

The term “defect site”, as used herein, refers to a defect in a crystallattice where the local crystal structure does not correspond to thecrystal structure of the bulk material. Defect sites include pointdefects, line defects and planar defects. Point defects include vacancydefects (the absence of an ion), interstitial defects (the interstitialinclusion of an additional ion), Frenkel defects (a closely located pairof defects consisting of an interstitial defect and a vacancy defect)and the presence of an impurity ion. Planar defects include grainboundaries, and stacking faults.

The term “grain boundary”, as used herein, refers to is a planar defectthat separates regions of different crystalline orientation (i.e.grains) within a crystalline solid. A grain boundary is therefore theinterface between two adjacent grains, or crystallites, in a crystallinematerial. Grain boundary defects can decrease the electrical and thermalconductivity of the material and are also preferred sites for the onsetof corrosion.

The term “organic compound” takes its normal meaning in the art.Typically, an organic compound will comprise a carbon atom. As theskilled person would understand it, an organic compound may comprise acarbon atom covalently bonded to another carbon atom, or to a hydrogenatom, or to a halogen atom, or to a chalcogen atom (for instance anoxygen atom, a sulfur atom, a selenium atom, or a tellurium atom). Thus,the term “organic compound” includes compounds such as perhalogenatedorganic compounds such as tetraiodomethane and iodopentafluorbenzene,and compounds such as oxalic acid, urea and thiourea. The skilled personwill understand that the term “organic compound” does not typicallyinclude compounds that are predominantly ionic such as carbides, forinstance.

The term “thiol group”, as used herein, refers to the group —SH. Theterm “sulfide group”, as used herein, refers to the group —S—, i.e. asulfur atom bonded to two other groups, typically wherein the sulfuratom is bonded to two carbon atoms.

The term “electron withdrawing group”, as used herein, refers to a groupwhich withdraws electrons away from the moiety to which it is attached.Electron withdrawing groups often contain electronegative groups such ashalogen atoms, carbonyl groups, and nitro groups.

The term “alkyl”, as used herein, refers to a linear or branched chainsaturated hydrocarbon radical. An alkyl group may be a C₁₋₁₈ alkylgroup, a C₁₋₁₄ alkyl group, a C₁₋₁₀ alkyl group, a C₁₋₆ alkyl group or aC₁₋₄ alkyl group. Examples of a C₁₋₁₀ alkyl group are methyl, ethyl,propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl. Examples ofC₁₋₆ alkyl groups are methyl, ethyl, propyl, butyl, pentyl or hexyl.Examples of C₁₋₄ alkyl groups are methyl, ethyl, i-propyl, n-propyl,t-butyl, s-butyl or n-butyl. If the term “alkyl” is used without aprefix specifying the number of carbons anywhere herein, it has from 1to 6 carbons (and this also applies to any other organic group referredto herein).

The term “cycloalkyl”, as used herein, refers to a saturated orpartially unsaturated cyclic hydrocarbon radical. A cycloalkyl group maybe a C₃₋₁₀ cycloalkyl group, a C₃₋₈ cycloalkyl group or a C₃₋₆cycloalkyl group. Examples of a C₃₋₈ cycloalkyl group includecyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclohexenyl,cyclohex-1,3-dienyl, cycloheptyl and cyclooctyl. Examples of a C₃₋₆cycloalkyl group include cyclopropyl, cyclobutyl, cyclopentyl, andcyclohexyl.

The term “alkenyl”, as used herein, refers to a linear or branched chainhydrocarbon radical comprising one or more double bonds. An alkenylgroup may be a C₂₋₁₈ alkenyl group, a C₂₋₁₄ alkenyl group, a C₂₋₁₀alkenyl group, a C₂₋₆ alkenyl group or a C₂₋₄ alkenyl group. Examples ofa C₂₋₁₀ alkenyl group are ethenyl (vinyl), propenyl, butenyl, pentenyl,hexenyl, heptenyl, octenyl, nonenyl or decenyl. Examples of C₂₋₆ alkenylgroups are ethenyl, propenyl, butenyl, pentenyl or hexenyl. Examples ofC₂₋₄ alkenyl groups are ethenyl, i-propenyl, n-propenyl, s-butenyl orn-butenyl. Alkenyl groups typically comprise one or two double bonds.

The term “alkynyl”, as used herein, refers to a linear or branched chainhydrocarbon radical comprising one or more triple bonds. An alkynylgroup may be a C₂₋₁₈ alkynyl group, a C₂₋₁₄ alkynyl group, a C₂₋₁₀alkynyl group, a C₂₋₆ alkynyl group or a C₂₋₄ alkynyl group. Examples ofa C₂₋₁₀ alkynyl group are ethynyl, propynyl, butynyl, pentynyl, hexynyl,heptynyl, octynyl, nonynyl or decynyl. Examples of C₁₋₆ alkynyl groupsare ethynyl, propynyl, butynyl, pentynyl or hexynyl. Alkynyl groupstypically comprise one or two triple bonds.

The term “aryl”, as used herein, refers to a monocyclic, bicyclic orpolycyclic aromatic ring which contains from 6 to 14 carbon atoms,typically from 6 to 10 carbon atoms, in the ring portion. Examplesinclude phenyl, naphthyl, indenyl and indanyl groups. The term “arylgroup”, as used herein, includes heteroaryl groups. The term“heteroaryl”, as used herein, refers to monocyclic or bicyclicheteroaromatic rings which typically contains from six to ten atoms inthe ring portion including one or more heteroatoms. A heteroaryl groupis generally a 5- or 6-membered ring, containing at least one heteroatomselected from O, S, N, P, Se and Si. It may contain, for example, one,two or three heteroatoms. Examples of heteroaryl groups include pyridyl,pyrazinyl, pyrimidinyl, pyridazinyl, furanyl, thienyl, pyrazolidinyl,pyrrolyl, oxazolyl, oxadiazolyl, isoxazolyl, thiadiazolyl, thiazolyl,isothiazolyl, imidazolyl, pyrazolyl, quinolyl and isoquinolyl.

The terms “alkylene”, “cycloalkylene”, “alkenylene”, “alkynylene”, and“arylene”, as used herein, refer to bivalent groups obtained by removinga hydrogen atom from an alkyl, cycloalkyl, alkenyl, alkynyl, or arylgroup, respectively. An alkylene group may be a C₁₋₁₈ alkylene group, aC₁₋₁₄ alkylene group, a C₁₋₁₀ alkylene group, a C₁₋₆ alkylene group or aC₁₋₄ alkylene group. Examples of C₁₋₆ alkylene groups are methylene,ethylene, propylene, butylene, pentylene and hexylene. A cycloalkylenegroup may be a C₃₋₁₀ cycloalkylene group, a C₃₋₈ cycloalkylene group ora C₃₋₆ cycloalkylene group. Examples of C₃₋₆ cycloalkylene groupsinclude cyclopentylene and cyclohexylene. An alkenylene group may be aC₂₋₁₈ alkenylene group, a C₂₋₁₄ alkenylene group, a C₂₋₁₀ alkenylenegroup, a C₂₋₆ alkenylene group or a C₂₋₄ alkenylene group. Examples of aC₂₋₄ alkenylene group include ethenylene (vinylene), propenylene andbutenylene. An alkynylene group may be a C₂₋₁₈ alkynylene group, a C₂₋₁₄alkynylene group, a C₂₋₁₀ alkynylene group, a C₂₋₆ alkynylene group or aC₂₋₄ alkynylene group. Examples of a C₂₋₄ alkynylene group includeethynylene and propynylene. Examples of arylene groups include phenyleneand a diradical derived from thiophene. For alkylene, cycloalkylene,alkenylene, alkynylene, and arylene, these groups may be bonded to othergroups at any two positions on the group. Thus, propylene includes—CH₂CH₂CH₂— and —CH₂CH(CH₃)—, and phenylene includes ortho-, meta- andpara-phenylene.

The term “substituted”, as used herein in the context of substitutedorganic groups, refers to an organic group which bears one or moresubstituents selected from C₁₋₁₀ alkyl, aryl (as defined herein), cyano,amino, nitro, C₁₋₁₀ alkylamino, di(C₁₋₁₀)alkylamino, arylamino,diarylamino, aryl(C₁₋₁₀)alkylamino, amido, acylamido, hydroxy, oxo,halo, carboxy, ester, acyl, acyloxy, C₁₋₁₀ alkoxy, aryloxy,halo(C₁₋₁₀)alkyl, sulfonic acid, thiol, C₁₋₁₀ alkylthio, arylthio,sulfonyl, phosphoric acid, phosphate ester, phosphonic acid andphosphonate ester. Examples of substituted alkyl groups includehaloalkyl, perhaloalkyl, hydroxyalkyl, aminoalkyl, alkoxyalkyl andalkaryl groups. When a group is substituted, it may bear 1, 2 or 3substituents. For instance, a substituted group may have 1 or 2substitutents.

The term “perhaloalkyl”, as used herein, refers to an alkyl group inwhich all, or almost all, H atoms have been replaced with halogen atoms.Typically, 3 out of 5 hydrogen atoms have been replaced with halogenatoms. Thus, perhaloalkyl groups include —(CF₂)₃F, —(CCl₂)₂(CF₂)₂H, and—(CHCl)(CF₂)H, for instance.

The term “oligomer”, as used herein, refers to a molecule whichcomprises a small number of repeating units (i.e. a small number ofmonomers). Typically oligomers comprise from 2 to 9 monomers, or from 3to 6 monomers.

The term “band gap”, as used herein, refers to the energy differencebetween the top of the valence band and the bottom of the conductionband in a material. The skilled person may readily measure the band gapof a material without undue experimentation.

The term “layer”, as used herein, refers to any structure which issubstantially laminar in form (for instance extending substantially intwo perpendicular directions, but limited in its extension in the thirdperpendicular direction). A layer may have a thickness which varies overthe extent of the layer. Typically, a layer has approximately constantthickness. The “thickness” of a layer, as used herein, refers to theaverage thickness of a layer. The thickness of layers may easily bemeasured, for instance by using microscopy, such as electron microscopyof a cross section of a film, or by surface profilometry for instanceusing a stylus profilometer.

The term “porous”, as used herein, refers to a material within whichpores are arranged. Thus, for instance, in a porous material the poresare volumes within the scaffold where there is no material. Pores in amaterial may include “closed” pores as well as open pores. A closed poreis a pore in a material which is a non-connected cavity, i.e. a porewhich is isolated within the material and not connected to any otherpore and which cannot therefore be accessed by a fluid to which thematerial is exposed. An “open pore” on the other hand, would beaccessible by such a fluid. The concepts of open and closed porosity arediscussed in detail in J. Rouquerol et al., “Recommendations for theCharacterization of Porous Solids”, Pure & Appl. Chem., Vol. 66, No. 8,pp. 1739-1758, 1994. Open porosity, therefore, refers to the fraction ofthe total volume of the porous material in which fluid flow couldeffectively take place. It therefore excludes closed pores. The term“open porosity” is interchangeable with the terms “connected porosity”and “effective porosity”, and in the art is commonly reduced simply to“porosity”. The term “without open porosity”, as used herein, thereforerefers to a material with no effective porosity. The term “non-porous”as used herein, refers to a material without any porosity, i.e. withoutopen porosity and also without closed porosity.

The term “semiconductor”, as used herein, refers to a material withelectrical conductivity intermediate in magnitude between that of aconductor and a dielectric. A semiconductor may be an n-typesemiconductor, a p-type semiconductor or an intrinsic semiconductor.

The term “n-type region”, as used herein, refers to a region of one ormore electron-transporting (i.e. n-type) materials. Similarly, the term“n-type layer” refers to a layer of an electron-transporting (i.e. ann-type) material. An electron-transporting (i.e. an n-type) materialcould be a single electron-transporting compound or elemental material,or a mixture of two or more electron-transporting compounds or elementalmaterials. An electron-transporting compound or elemental material maybe undoped or doped with one or more dopant elements.

The term “p-type region”, as used herein, refers to a region of one ormore hole-transporting (i.e. p-type) materials. Similarly, the term“p-type layer” refers to a layer of a hole-transporting (i.e. a p-type)material. A hole-transporting (i.e. a p-type) material could be a singlehole-transporting compound or elemental material, or a mixture of two ormore hole-transporting compounds or elemental materials. Ahole-transporting compound or elemental material may be undoped or dopedwith one or more dopant elements.

The term “treating”, as used herein, refers to any process in which onecompound is allowed to react or interact with another. One of thecompounds with which the other is treated may be added as the compounditself, or may be added as a precursor that converts by some process tothe compound itself.

The term “disposing on”, as used herein, refers to the making availableor placing of one component on another component. The first componentmay be made available or placed directly on the second component, orthere may be a third component which intervenes between the first andsecond component. For instance, if a first layer is disposed on a secondlayer, this includes the case where there is an intervening third layerbetween the first and second layers. Typically, however, “disposing on”refers to the direct placement of one component on another.

The term “electrode material”, as used herein, refers to any materialsuitable for use in an electrode. An electrode material will have a highelectrical conductivity.

Device

In a first aspect the invention provides a device comprising asemiconductor, which semiconductor comprises:

-   -   (a) a metal halide perovskite; and    -   (b) a passivating agent which is an organic compound;        wherein molecules of the passivating agent are chemically bonded        to anions or cations in the metal halide perovskite. The metal        halide perovskite may be an organometal halide perovskite.

Usually, the semiconductor in the devices and processes of the firstembodiment of the invention comprises (a) said metal halide perovskite,in addition to (b) the passivating agent, and the invention willgenerally be described hereinbelow in those terms. However, as mentionedabove, the invention is applicable not just to metal halide perovskitesemiconductors but to crystalline ionic solid semiconductors in general,including crystalline ionic solid semiconductors other than metal halideperovskites, such as for instance metal oxide semiconductors. Metaloxide semiconductors are themselves well known and titania is oneexample of such a metal oxide semiconductor. Accordingly, as the skilledperson will appreciate, any of the embodiments of the inventiondescribed hereinbelow in terms of a metal halide perovskite may also beperformed using any ionic crystalline solid, such as for instance ametal oxide, e.g. titania. Usually, the crystalline ionic solid is ametal halide perovskite, which may for instance be any of the metalhalide perovskites described or defined further herein. Alternatively,however, the crystalline ionic solid may comprise a differentcrystalline ionic solid, for instance a metal oxide. One metal oxidethat is often employed is titanium dioxide.

Thus, in another aspect, the first aspect of the invention provides adevice comprising a semiconductor, which semiconductor comprises: (a) acrystalline ionic solid; and (b) a passivating agent which is an organiccompound; wherein molecules of the passivating agent are chemicallybonded to anions or cations in the crystalline ionic solid.

When the device comprises a crystalline ionic solid, the crystallineionic solid may comprise any ionic solid defined anywhere herein. Forinstance, the crystalline ionic solid may comprise an inorganic n-typematerial or an inorganic p-type material as described herein, inparticular a crystalline inorganic n-type material. Thus, thecrystalline ionic solid may comprise a metal oxide. The device maycomprise a semiconductor, which semiconductor comprises: (a) an metaloxide; and (b) a passivating agent which is an organic compound; whereinmolecules of the passivating agent are chemically bonded to anions orcations in the metal oxide. The metal oxide is often an oxide oftitanium, tin, zinc, niobium, tantalum, tungsten, indium, gallium,neodinium, palladium, or cadmium, or an oxide of a mixture of two ormore of said metals. For instance, the ionic solid may be a metal oxideselected from TiO₂, SnO₂, ZnO, Nb₂O₅, Ta₂O₅, WO₃, W₂O₅, In₂O₃, Ga₂O₃,Nd₂O₃, PbO, and CdO. In particular, the metal oxide may be TiO₂. Thecrystalline ionic solid may comprise an inorganic p-type material suchas any of those described herein. The crystalline ionic solid maycomprise a semiconducting metal halide or a semiconducting compoundcomprising copper. For instance, the crystalline ionic solid maycomprise CuI, CuBr, CuSCN, Cu₂O, CuO or CIS.

In the first aspect the passivating agent is an organic compound. Thepassivating agent may be an organic compound having a molecular weightof less than or equal to 2000 gmol⁻¹, or less than or equal to 1000gmol⁻¹. The passivating agent may be an organic compound comprising oneor more heteroatoms. The passivating agent is typically an organiccompound comprising from one 10 to heteroatoms, or comprising from oneto six heteroatoms. The heteroatoms are usually selected from thep-block of the Periodic Table (except for C). For instance, the one ormore heteroatoms may be independently selected from N, P, As, O, S, Se,Te, F, Cl, Br, and I. Usually, the one or more heteroatoms are eachindependently selected from N, P, O, S, Se, Te, F, Cl, Br, and ITypically, the one or more, or one to six, heteroatoms may beheteroatoms each independently selected from N, O, S, Se, Te, F, Cl, Br,and I, for instance O, S, F, Cl, Br and I or N, S, F, Cl, Br, and I. Thepassivating agent is typically an organic compound, which organiccompound comprises one or more atoms selected from O, S, F, Cl, Br andI. The passivating agent may be an organic compound, which organiccompound comprises one or more atoms selected from S, F, Cl, Br and I.The organic compound may comprise one or more different types ofheteroatom.

In the first aspect the passivating agent may be an organic compound,which organic compound comprises one or more atoms selected from N, P,S, F, Cl, Br and I. The passivating agent may be an organic compound,which organic compound comprises one or more atoms selected from N, Pand S. In one embodiment, the passivating agent is an organic compound,which organic compound comprises one or more atoms selected from N andP.

In the first aspect, at least some of the molecules of the passivatingagents are chemically bonded to anions or cations in the metal halideperovskite. Typically, the molecules of the passivating agent arechemically bonded to anions or cations in the metal halide perovskite bysupramolecular chemical bonds. All, or essentially all, of the moleculesof the passivating agent may be bonded to anions or cations in the metalhalide perovskite. Greater than or equal to 50%, or greater than orequal to 70% of the molecules of the passivating agent are typicallybonded to anions or cations in the metal halide perovskite. Forinstance, greater than or equal to 90% of the molecules of thepassivating agent are typically bonded to anions or cations in the metalhalide perovskite. Molecules of the passivating agent are often bondedto anions or cations in the metal halide perovskite via heteroatoms inthe molecules of the passivating agent. The word “bonded” may be usedinterchangeably with “bound”.

The chemical bonds are typically supramolecular chemical bonds. Thus,the semiconductor may comprise: (a) a metal halide perovskite; and (b) apassivating agent which is an organic compound; wherein molecules of thepassivating agent are supramolecularly chemically bonded to anions orcations in the metal halide perovskite.

The chemical bonds between molecules of the passivating agent and anionsor cations in the metal halide perovskite are usually selected fromhalogen bonds and chalcogen-metal bonds. Chalcogen-metal bonds may beselected from oxygen-metal bonds, sulfur-metal bonds, or selenium-metalbonds. Typically, the chalcogen-metal bonds are sulfur-metal bonds. Thechalcogen-metal bonds may be dative covalent bonds.

The chemical bonds between molecules of the passivating agent and anionsor cations in the metal halide perovskite may alternatively be selectedfrom nitrogen-metal bonds and phosphorus-metal bonds. In anitrogen-metal bond, a nitrogen atom in the passivating agent maycoordinate to the metal ion or atom through a lone pair. Thenitrogen-metal bonds may be dative covalent bonds. In a phosphorus-metalbond, a phosphorus atom in the passivating agent may coordinate to themetal ion or atom through a lone pair. The phosphorus-metal bonds may bedative covalent bonds. Both nitrogen-metal bonds and phosphorus metalbonds are typically supramolecular bonds.

Cations or anions in the metal halide perovskite to which molecules ofthe passivating agent are bonded are typically under-coordinated.Under-coordinated anions and cations may be located at an exposedsurface of the perovskite, or may be in the bulk of the perovskite at ornear a defect site. Under-coordinated anions or cations may beunder-coordinated due to the absence of one, two, three or four nearestneighbour counterions.

At least some of the anions or cations in the metal halide perovskite towhich molecules of the passivating agent are bonded may be at thesurface of the metal halide perovskite or at defect sites in bulk of thecrystal structure of the metal halide perovskite. Often, anions orcations in the metal halide perovskite to which molecules of thepassivating agent are bonded are at the surface of the metal halideperovskite and at the grain boundaries in bulk of the metal halideperovskite.

In a second aspect, the invention provides a device comprising asemiconductor, which semiconductor comprises:

-   -   (a) a metal halide perovskite; and    -   (b) a passivating agent which is an organic compound;        wherein molecules of the passivating agent are disposed at grain        boundaries within the metal halide perovskite and are not        chemically bonded to anions or cations in the metal halide        perovskite. The metal halide perovskite may be an organometal        halide perovskite. The device may be an optoelectronic device,        for instance a photovoltaic device.

The second aspect of the invention therefore also provides a devicecomprising a semiconductor, which semiconductor comprises: (a) acrystalline ionic solid; and (b) a passivating agent which is an organiccompound; wherein molecules of the passivating agent are disposed atgrain boundaries within the crystalline ionic solid and are notchemically bonded to anions or cations in the crystalline ionic solid.

In the second aspect the passivating agent may be an organic compound,which organic compound comprises non-polar organic molecules. Thepassivating agent may be an organic compound, which organic compoundcomprises polycyclic aromatic hydrocarbon molecules.

Passivating Agents and Passivation

As described above, in the first aspect the passivating agent which isan organic compound is typically an organic compound comprising one ormore heteroatoms. The passivating agent may be an organic compoundcomprising a heteroatom which has a lone pair. A lone pair may interactwith an ion in the metal halide perovskite to form a chemical bond, forinstance a supramolecular bond such as a dative bond.

Typically, the formula of the metal halide perovskite contains acompound A or a cation of a compound AH⁺, the passivating agent will notbe the compound A. Thus, if the formula of the metal halide perovskiteincludes a specific alkyl ammonium ion, the passivating agent of thefirst aspect is not the corresponding alkyl amine.

In the first aspect the passivating agent may be a compound selectedfrom: (a) a halogen bond donor compound, and (b) an organic compoundcomprising at least one heteroatom with a lone pair. The organiccompound comprising at least one heteroatom with a lone pair may beselected from an organic compound comprising at least one heteroatomselected from N, P, As, O, S, Se and Te. The organic compound comprisingat least one heteroatom with a lone pair is typically selected from anorganic compound comprising at least one hetero atom selected from N, P,O, S and Se or selected from N, O and S. The passivating agent may be acompound selected from: (a) a halogen bond donor compound, and (b) anorganic compound comprising at least one heteroatom selected from N, P,As, O, S, Se and Te. The passivating agent may be a compound selectedfrom: (a) a halogen bond donor compound, and (b) an organic compoundcomprising at least one heteroatom selected from N, P, O, S, and Se, orN, O, and S.

Examples of compounds comprising at least one N include compoundscomprising a group selected from amine, imine, nitrile, hydrazine,pyridine, 2H-pyrrole, pyrrole, 2-pyrroline, 3-pyrroline, pyrrolidine,oxazole, thiazole, imidazole, 2-imidazoline, imidazolidine, pyrazole,2-pyrazoline, and other nitrogen containing heterocycles. For instance,a compound comprising at least one N may be a compound comprising agroup selected from amine, imine, nitrile, hydrazine, pyridine, andpyrrolidine. Thus, the passivating agent may be a substituted orunsubstituted amine, a substituted or unsubstituted imine, a substitutedor unsubstituted pyridine or a substituted or unsubstituted pyrrolidine.

In a device according to the first aspect of the invention, thepassivating agent may be a compound selected from: (a) a halogen bonddonor compound, and (b) an organic compound comprising at least onethiol or sulfide group. The passivating agent may be an organic compoundcomprising at least one heteroatom selected from N and P.

The passivating agent of the first aspect may be a halogen bond donorcompound. The passivating agent may be an organic compound comprising atleast one thiol or sulfide group. The device may comprise furtherpassivating agents. Thus, the device may further comprise a secondpassivating agent. For instance, the device may comprises a firstpassivating agent which is a halogen bond donor compound and a secondpassivating agent which is an organic compound comprising at least onethiol or sulfide group.

The passivating agent of the first aspect may be a halogen bond donorcompound of formula X-EWG, wherein: X is a halogen selected from I, Br,Cl and F; and EWG is an electron withdrawing group. EWG may be any groupwhich inductively or conjugatively withdraws electrons from X. EWG maybe an organic group comprising one or more atoms having anelectronegativity greater than that of carbon. EWG may comprise one ormore, two or more, three or more, or from three to six atoms having aPauling electronegativity of greater than or equal to 2.6. EWG maycomprise one or more, two or more, three or more, or from three to sixatoms having a Pauling electronegativity of greater than or equal to2.9. The atoms having a Pauling electronegativity of greater than orequal to 2.6, or greater than or equal to 2.9, may be separated from Xby 10 or less, or 6 or less, bonds. Tables of Pauling electronegativityvalues are available to the skilled person. Pauling electronegativityvalues include 2.98 for F, 3.44 for O, 3.16 for Cl, 3.04 for N, and 2.96for Br. EWG may be an organic group comprising two or more, three ormore, four or more or five or more atoms selected from F, Cl, Br, I, O,and S. EWG may be a perhalo-C₁₋₁₂-alkyl group. For instance, EWG may bea perfluoro-C₁₋₁₂-alkyl group, such as trifluormethyl, pentafluoroethyl,or heptafluoropropyl, perfluorobutyl, perfluoropentyl, perfluorohexyl,perfluoroheptyl, perfluorooctyl, perfluorononyl or perfluorodecyl.

X may be selected from I, Br, Cl and F, from I, Br and Cl, or from I andBr. For instance, X may be I.

The passivating agent of the first aspect is often a halogen bond donorcompound of formula X-EWG, wherein

-   -   X is a halogen selected from I, Br, Cl and F; and    -   EWG is a group selected from —(CY₂)_(n)Y, —(CY₂)_(n)R,        —(CR₂)_(n)Y, —(CR₂)_(n)R, —(CY₂)_(n)CR₃, —(CR₂)_(n)CY₃,        —(CY₂)_(n)(CR₂)_(m)Y, —(CR₂)_(n)(CY₂)_(m)Y,        —(CY₂)_(n)(CR₂)_(m)R, —(CR₂)_(n)(CY₂)_(m)R,        —(CY₂)_(n)(CR₂)_(m)CY₃, —(CR₂)_(n)(CY₂)_(m)CR₃,        —(CR_(a)Y_(b))_(n)Y, —(CR_(a)Y_(b))_(n)R, —C₆Y₅, —(C₆R)Y₄,        —(C₆R₂)Y₃, —(C₆R₃)Y₂, —(C₆R₄)Y, —CY═CYR, —CY═CR₂, —CR═CYR,        —C≡CY, —C≡CR, —COR, —COCYR₂ and —COCY₂R; wherein    -   each Y is the same or different and is a halogen selected from        I, Br, Cl, and F;    -   each R is the same or different and is a group selected from H,        hydroxy, nitrile, nitro, unsubstituted or substituted        C₁₋₁₈-alkyl, unsubstituted or substituted C₃₋₁₀-cycloalkyl,        unsubstituted or substituted C₂₋₁₈-alkenyl, unsubstituted or        substituted C₂₋₁₈-alkynyl, and unsubstituted or substituted        aryl;    -   n is an integer from 1 to 18;    -   m is an integer from 1 to 18;    -   each a is the same or different and is 0, 1 or 2;    -   each b is the same or different and is 0, 1 or 2; and the sum of        a and b in each CR_(a)Y_(b) group is 2.

Thus, the groups —(CR_(a)Y_(b))_(n)Y and —(CR_(a)Y_(b))_(n)R include anystraight chain alkyl group substituted with any number of halogen atoms.For instance, —(CR_(a)Y_(b))_(n)Y includes —(CClH)(CH₂)₂(CFI)Br and—(CHF)₃CF₃.

Often n is an integer from 1 to 6 and m is an integer from 1 to 6. EWGmay be a group selected from —(CY₂)_(n)Y, —(CY₂)_(n)R, —(CR₂)_(n)Y,—(CR₂)_(n)R, —(CY₂)_(n)CR₃, —(CR₂)_(n)CY₃, —(CY₂)_(n)(CR₂)_(m)Y,—(CR₂)_(n)(CY₂)_(m)Y, —(CY₂)_(n)(CR₂)_(m)R, —(CR₂)_(n)(CY₂)_(m)R,—(CY₂)_(n)(CR₂)_(m)CY₃, —(CR₂)_(n)(CY₂)_(m)CR₃, —(CR_(a)Y_(b))_(n)Y,—(CR_(a)Y_(b))_(n)R, —C₆Y₅, —(C₆R)Y₄, —(C₆R₂)Y₃, —(C₆R₃)Y₂, —(C₆R₄)Y,—CY═CYR, —CY═CR₂, —CR≡CYR, —C≡CY, —C≡CR, —COR, —COCYR₂ and —COCY₂R;wherein each Y is the same or different and is a halogen selected fromI, Br, Cl, and F; each R is the same or different and is a groupselected from H, hydroxy, nitrile, nitro, unsubstituted or substitutedC₁₋₁₈-alkyl, unsubstituted or substituted C₃₋₁₀-cycloalkyl,unsubstituted or substituted C₂₋₁₈-alkenyl, unsubstituted or substitutedC₂₋₁₈-alkynyl, and unsubstituted or substituted aryl; n is an integerfrom 1 to 6; m is an integer from 1 to 6; each a is the same ordifferent and is 0, 1 or 2; each b is the same or different and is 0, 1or 2; and the sum of a and b in each CR_(a)Y_(b) group is 2. Often, R isunsubstituted. Each R is the same or different and is usually a groupselected from H, hydroxy, nitrile, nitro, unsubstituted C₁₋₁₀-alkyl,unsubstituted C₃₋₁₀-cycloalkyl, unsubstituted C₂₋₁₀-alkenyl,unsubstituted C₂₋₁₀-alkynyl, and unsubstituted aryl.

The passivating agent of the first aspect may be a halogen bond donorcompound of formula X-EWG, wherein X is a halogen selected from I, Br,Cl and F; and EWG is a group selected from —CY₃, —(CY₂)₂Y, —(CY₂)₃Y,—CY₂R, —(CY₂)₂R, —(CY₂)₃R, —CR₂Y, —C₆Y₅, —(C₆R)Y₄, —(C₆R₂)Y₃, —(C₆R₃)Y₂,—(C₆R₄)Y, —CY═CYR, —CY═CR₂, —C≡CY, —COR, —COCYR₂ and —COCY₂R; whereineach Y is the same or different and is a halogen selected from I, Br,Cl, and F; and each R is the same or different and is a group selectedfrom H, hydroxy, nitrile, nitro, unsubstituted or substitutedC₁₋₁₈-alkyl, unsubstituted or substituted C₃₋₁₀-cycloalkyl,unsubstituted or substituted C₂₋₁₈-alkenyl, unsubstituted or substitutedC₂₋₁₈-alkynyl, and unsubstituted or substituted aryl.

EWG may be a group selected from —CY₃, —(CY₂)₂Y, —(CY₂)₃Y, —(CY₂)₂R,—(CY₂)₃R, —C₆Y₅, —(C₆R)Y₄, —(C₆R₂)Y₃, —COR, —COCYR₂ and —COCY₂R. X maybe selected from I, Br and Cl. Y may be selected from I, Br, Cl, and F,from Br, Cl and F, or from Cl and F. For instance, Y may be F. X may beselected from I and Br and Y may be selected from Cl and F.

The passivating agent of the first aspect is often a halogen bond donorcompound selected from X(CY₂)_(m)CY₃ and

wherein X is a halogen selected from I, Br, Cl and F; each Y is the sameor different and is a halogen selected from I, Br, Cl and F; m is 0 oran integer from 1 to 11 and n is an integer from 1 to 5.

The passivating agent of the first aspect may be a halogen bond donorcompound selected from I(CY₂)_(m)CY₃ and

wherein each Y is the same or different and is a halogen selected fromI, Br, Cl and F; m is 0 or an integer from 1 to 11 and n is an integerfrom 1 to 5.

The passivating agent of the first aspect may be a halogen bond donorcompound selected from I(CF₂)_(m)CF₃ and

wherein m is 0 or an integer from 1 to 11; and n is an integer from 1 to5.

Often, m is from 0 to 8. Typically, n is from 2 to 5. Typically, X isselected from I or Br and Y may be selected from Br, Cl and F.

The passivating agent of the first aspect may be selected fromiodopentafluorbenzene, iodotetrafluorobenzene,iodochlorotetrafluorobenzene, iododichlorotrifluorobenzene,iodochlorotrifluorobenzene, iodotrifluorobenzene,iododichlorodifluorobenzene, and iododifluorobenzene, for instance.

The passivating agent of the first aspect may be selected fromiodopentafluorobenzene and a perfluoro-C₁₋₁₂alkyl iodine. Often, thepassivating agent is selected from iodopentafluorobenzene,perfluoro-n-butyl iodine, perfluoro-n-hexyl iodine, andperfluoro-n-decyl iodine. Iodopentafluorobenzene has the formula IC₆F₅.

The passivating agent of the first aspect may be an organic moleculewhich is suitable for forming a chalcogen-metal bond with metal ions inthe perovskite. Thus, the passivating agent may be an organic moleculewhich comprises a chalcogen atom. The passivating agent may be acompound which comprises one or more, for instance two or more,chalcogen atoms. For instance, the passivating agent may be an organiccompound which comprises a hydroxy group, a compound which comprises anether group, an organosulfur compound, an organoselenium compound, or anorganotellurium compound. Thus, the passivating agent may be anorganosulfur compound or an organoselenium compound. Often thepassivating agent is an organosulfur compound.

Examples of organosulfur compounds include compounds comprising one ormore groups selected from thioether (sulfide), thioester, thioacetal,thiol, disulfide, sulfone, thiosulfinate, thioketone, and thioaldehyde.Examples of organosulfur compounds include compounds comprising athiophene, dihydrothiophene, tetrahydrothiophene, or tetrathiafulvalenegroup. Organoselenium and organosulfur compounds include those derivedby replacing one or more sulfur atoms in an organosulfur compound withselenium or tellurium respectively.

The passivating agent of the first aspect may be an organic compoundcomprising at least one thiol or sulfide group. The passivating agentmay be an organic compound comprising one thiol or sulfide group. Thepassivating agent may be an organic compound comprising two or morethiol or sulfide groups. The passivating agent may be an oligomer or apolymer, which oligomer or polymer comprises at least one thiol orsulfide group. If the passivating agent is an oligomer or a polymer, theoligomer or polymer may comprise monomers which comprise a thiophenering. If the passivating agent is an oligomer, it may have from 2 to 9repeating units, from 2 to 8 repeating units, or from 3 to 6 repeatingunits. The repeating units may comprise thiophene ortetrahydrothiophene. The passivating agent may be selected fromsexithiophene. If the passivating is a polymer, it has greater than orequal to 10 repeating units. However, often the passivating agent is nota polymer. Thus, in one embodiment, the passivating agent, which is anorganic compound, is not a polymer. Polymers typically have highmolecular weights. Accordingly, the passivating agent which is anorganic compound, may be an organic compound having a molecular weightof less than or equal to 2000 gmol⁻¹, or less than or equal to 1000gmol⁻¹. In some cases, the passivating agent may be a monomeric organiccompound which does not comprise a repeating unit.

The passivating agent of the first aspect may be an organic compoundcomprising at least one thiol or sulfide group, selected from: (i) R¹SH,R¹SR¹, HSR²SH, R¹SR²SR¹, R¹SR²SH,

wherein: each R¹ is the same or different and is a group selected fromunsubstituted or substituted C₁₋₁₈-alkyl, unsubstituted or substitutedC₃₋₁₀-cycloalkyl, unsubstituted or substituted C₂₋₁₈-alkenyl,unsubstituted or substituted C₂₋₁₈-alkynyl, and unsubstituted orsubstituted aryl; R² is a group selected from unsubstituted orsubstituted C₁₋₁₈-alkylene, unsubstituted or substitutedC₃₋₁₀-cycloalkylene, unsubstituted or substituted C₂₋₁₈-alkenylene,unsubstituted or substituted C₂₋₁₈-alkynylene, and unsubstituted orsubstituted arylene; and each R³ is the same or different and is a groupselected from H, hydroxy, nitrile, nitro, halo, thiol, amino,unsubstituted or substituted C₁₋₁₈-alkyl, unsubstituted or substitutedC₃₋₁₀-cycloalkyl, unsubstituted or substituted C₂₋₁₈-alkenyl,unsubstituted or substituted C₂₋₁₈-alkynyl, and unsubstituted orsubstituted aryl; and (ii) an oligomer, which oligomer comprises atleast one thiol or sulfide group.

Each R¹ is the same or different and may be a group selected fromunsubstituted or substituted C₁₋₆-alkyl, unsubstituted or substitutedC₃₋₆-cycloalkyl, unsubstituted or substituted C₂₋₆-alkenyl,unsubstituted or substituted C₂₋₆-alkynyl, and unsubstituted orsubstituted aryl. R¹ may be unsubstituted. R² may be a group selectedfrom unsubstituted or substituted C₁₋₆-alkylene, unsubstituted orsubstituted C₃₋₆-cycloalkylene, unsubstituted or substitutedC₂₋₆-alkenylene, unsubstituted or substituted C₂₋₆-alkynylene, andunsubstituted or substituted arylene. R² may be unsubstituted. Each R³is the same or different and may be a group selected from H, hydroxy,nitrile, nitro, halo, amino, thiol, unsubstituted or substitutedC₁₋₆-alkyl, unsubstituted or substituted C₃₋₆-cycloalkyl, unsubstitutedor substituted C₂₋₆-alkenyl, unsubstituted or substituted C₂₋₆-alkynyl,and unsubstituted or substituted aryl. R³ may be unsubstituted. One, twoor three of R³ may be H.

The passivating agent of the first aspect may be an organic compoundcomprising at least one thiol or sulfide group, selected from:

wherein: each R³ is the same or different and is a group selected fromH, hydroxy, nitrile, nitro, halo, thiol, amino, unsubstituted orsubstituted C₁₋₁₈-alkyl, unsubstituted or substituted C₃₋₁₀-cycloalkyl,unsubstituted or substituted C₂₋₁₈-alkenyl, unsubstituted or substitutedC₂₋₁₈-alkynyl, and unsubstituted or substituted aryl; and each R is thesame or different and is a group selected from H, hydroxy, nitrile,nitro, halo, thiol, amino, unsubstituted or substituted C₁₋₁₈-alkyl,unsubstituted or substituted C₃₋₁₀-cycloalkyl, unsubstituted orsubstituted C₂₋₁₈-alkenyl, unsubstituted or substituted C₂₋₁₈-alkynyl,and unsubstituted or substituted aryl.

The passivating agent of the first aspect may be a thiol, such asmethanethiol, ethanethiol, propanethiol, butanethiol and pentanethiol.The passivating agent may be a dithiol, such as ethanedithiol,propanedithiol and butanedithiol. Often, the passivating agent is acompound comprising a heteroaryl group, which heteroaryl group comprisesa sulfur atom. The passivating agent may comprise a thiophene group, adithiophene group, or a thiazole group.

The passivating agent of the first aspect may be selected from thiopheneor tetrahydrothiophene substituted with one, two, three or fourunsubstituted or substituted C₁₋₆-alkyl groups. The passivating agentmay be selected from thiophene, tetrahydrothiophene, and3-C₁₋₆-alkylthiophenes. The passivating agent may be thiophene,3-hexylthiophene or tetrahydrothiophene. The passivating agent is oftenthiophene or tetrahydrothiophene.

Molecules of the passivating agent of the first aspect formsupramolecular chemical bonds with anions and cations in the metalhalide perovskite. The formation of these supramolecular bonds (forinstance halogen bonds and chalogen-metal bonds) can order the moleculesof the passivating agent. The molecules of the passivating agent may beordered into regular layers.

Molecules of the passivating agent of the first aspect often form aself-assembled layer on a surface of the metal halide perovskite.Molecules of the passivating agent may form a monolayer on a surface ofthe perovskite. Molecules of the passivating agent may form aself-assembled monolayer. Molecules of the passivating agent may form amonolayer on a surface of the perovskite with a coverage of from 10% to100%, from 50% to 100%, or from 80% to 100%. The coverage may bemeasured by standard techniques, for instance dual polarisationinterferometry.

Molecules of the passivating agent of the first aspect may be bonded tounder-coordinated cations or under-coordinated anions in the bulk of thecrystal structure of the metal halide perovskite. As discussed above inthe definition of “defect site”, several types of defects may leaveunder-coordinated anions and cations in the bulk of the perovskite.These internal defect sites may also reduce device efficiency. Moleculesof the passivating agent may be small enough to enter the bulk of thecrystal structure of the metal halide perovskite. For instance,molecules of the passivating agent may have a largest external width ofless than or equal to 1 nm. Molecules of the passivating agent of thefirst aspect may also be bonded to cations or anions at grain boundariesin the bulk of the crystal structure of the metal halide perovskite. Thepassivating agent of the first aspect is often a halogen bond donorcompound, and molecules of the halogen bond donor compound may be bondedto halide anions in the metal halide perovskite by halogen bonding. Thepassivating agent of the first aspect is often an organic compoundcomprising at least one thiol or sulfide group, and molecules of theorganic compound may be bonded to metal cations in the metal halideperovskite by sulfur-metal bonds.

The passivating agent of the first aspect may be an organic compoundcomprising at least one heteroatom selected from N and P. Thepassivating agent may, for instance, be an organic compound selectedfrom a substituted or unsubstituted amine, a substituted orunsubstituted imine, substituted or unsubstituted pyridine, substitutedor unsubstituted pyrrolidine, substituted or unsubstituted pyrrole and asubstituted or unsubstituted phosphine.

A substituted or unsubstituted amine is typically a substituted orunsubstituted primary amine, a substituted or unsubstituted secondaryamine, or a substituted or unsubstituted tertiary amine.

A substituted or unsubstituted primary amine may be a substituted orunsubstituted primary alkyl amine or a substituted or unsubstitutedprimary aryl amine. The passivating agent may therefore be a compound offormula RNH₂, wherein R is a group selected from substituted orunsubstituted C₁₋₁₈ alkyl and substituted or unsubstituted aryl. Forinstance, the passivating compound may be methylamine, ethylamine,propylamine, tertbutylamine or aniline. R may for instance be selectedfrom substituted or unsubstituted C₂₋₁₈ alkyl and substituted orunsubstituted aryl. The passivating compound may therefore beethylamine, propylamine, tertbutylamine or aniline.

A substituted or unsubstituted secondary amine may be a substituted orunsubstituted secondary alkyl amine (a dialkyl amine), a substituted orunsubstituted secondary aryl amine (an diaryl amine) or a substituted orunsubstituted secondary alkyl aryl amine. The passivating agent maytherefore be a compound of formula R₂NH, wherein each R is a groupindependently selected from substituted or unsubstituted C₁₋₁₈ alkyl orsubstituted or unsubstituted aryl, optionally wherein the two R groupsare bonded together to form a ring. For instance, the passivating agentmay be dimethylamine, diethylamine, dipropylamine, pyrrolidine,piperidine or diphenylamine. Substituted and unsubstituted secondaryamines thus include cyclic amines such as substituted or unsubstitutedpyrrolidine, substituted or unsubstituted piperidine, and substituted orunsubstituted morpholine.

A substituted or unsubstituted tertiary amine may be a substituted orunsubstituted tertiary alkyl amine (a trialkyl amine), a substituted orunsubstituted tertiary aryl amine (an triaryl amine) or a substituted orunsubstituted tertiary alkyl aryl amine (a dialkyl aryl amine or a alkyldiaryl amine). The passivating agent may therefore be a compound offormula R₃N, wherein each R is a group independently selected fromsubstituted or unsubstituted C₁₋₁₈ alkyl or substituted or unsubstitutedaryl, optionally wherein the two R groups are bonded together to form aring. For instance, the passivating agent may be trimethylamine,triethylamine, triphenylamine, N-methylpyrrolidine or quinuclidine.

Thus, the passivating agent of the first aspect may be an organiccompound of formula

wherein

-   -   R⁴, R⁵ and R⁶ are each independently a group selected from H,        unsubstituted or substituted C₁₋₁₈-alkyl, unsubstituted or        substituted C₃₋₁₀-cycloalkyl, unsubstituted or substituted        C₂₋₁₈-alkenyl, unsubstituted or substituted C₂₋₁₈-alkynyl, and        unsubstituted or substituted aryl, and not all R⁴, R⁵ and R⁶ are        H, optionally wherein two or more of R⁴, R⁵ and R⁶ are bonded        together to form a ring;    -   each R⁷ is independently a group selected from H, unsubstituted        or substituted C₁₋₁₈-alkyl, unsubstituted or substituted        C₃₋₁₀-cycloalkyl, unsubstituted or substituted C₂₋₁₈-alkenyl,        unsubstituted or substituted C₂₋₁₈-alkynyl, and unsubstituted or        substituted aryl, optionally wherein two or more R⁷ groups are        bonded together to form a ring;    -   R⁸ is a group selected from H, unsubstituted or substituted        C₁₋₁₈-alkyl, unsubstituted or substituted C₃₋₁₀-cycloalkyl,        unsubstituted or substituted C₂₋₁₈-alkenyl, unsubstituted or        substituted C₂₋₁₈-alkynyl;    -   R⁹, R¹⁰ and R¹¹ are each independently a group selected from H,        unsubstituted or substituted C₁₋₁₈-alkyl, unsubstituted or        substituted C₃₋₁₀-cycloalkyl, unsubstituted or substituted        C₂₋₁₈-alkenyl, unsubstituted or substituted C₂₋₁₈-alkynyl, and        unsubstituted or substituted aryl, optionally wherein two or        more of R⁹, R¹⁰ and R¹¹ are bonded together to form a ring; and    -   a dashed line together with a solid line may represent a single        or a double bond.

Typically, R⁴, R⁵ and R⁶ are each independently a group selected from H,unsubstituted or substituted C₁₋₆-alkyl, unsubstituted or substitutedC₃₋₆-cycloalkyl and unsubstituted or substituted aryl, and not all R⁴,R⁵ and R⁶ are H, optionally wherein two or more of R⁴, R⁵ and R⁶ arebonded together to form a ring.

Typically, each R⁷ is independently a group selected from H andunsubstituted or substituted C₁₋₆-alkyl, optionally wherein two or moreR⁷ groups are bonded together to form a ring.

Typically, R⁸ is a group selected from H and unsubstituted orsubstituted C₁₋₆-alkyl.

Typically, R⁹, R¹⁰ and R¹¹ are each independently a group selected fromH and unsubstituted or substituted C₁₋₆-alkyl, optionally wherein two ormore of R⁹, R¹⁰ and R¹¹ are bonded together to form a ring.

Preferably, R⁴, R⁵ and R⁶ are each independently a group selected from Hand unsubstituted or substituted C₁₋₃-alkyl, and not all R⁴, R⁵ and R⁶are H, optionally wherein two or more of R⁴, R⁵ and R⁶ are bondedtogether to form a ring. Often, at least one of R⁴, R⁵ and R⁶ is H.

Preferably, each R⁷ is independently a group selected from H andunsubstituted or substituted C₁₋₃-alkyl, optionally wherein two or moreR⁷ groups are bonded together to form a ring.

Preferably, R⁸ is a group selected from H and unsubstituted orsubstituted C₁₋₃-alkyl. R⁸ is often H.

Preferably, R⁹, R¹⁰ and R¹¹ are each independently a group selected fromH and unsubstituted or substituted C₁₋₃-alkyl, optionally wherein two ormore of R⁹, R¹⁰ and R¹¹ are bonded together to form a ring.

More preferably, R⁴, R⁵ and R⁶ are each independently a group selectedfrom H and unsubstituted methyl or ethyl, and not all R⁴, R⁵ and R⁶ areH, optionally wherein two or more of R⁹, R¹⁰ and R¹¹ are bonded togetherto form a ring. Often, at least one of R⁴, R⁵ and R⁶ is H.

More preferably, each R⁷ is independently a group selected from H andunsubstituted methyl or ethyl, optionally wherein two or more of R⁹, R¹⁰and R¹¹ are bonded together to form a ring.

More preferably, R⁸ is a group selected from H and unsubstituted orsubstituted methyl or ethyl.

More preferably, R⁹ and R¹⁰ are each independently a group selected fromH and unsubstituted methyl or ethyl, optionally wherein two or more ofR⁹ and R¹⁰ are bonded together to form a ring, and R¹¹ is H orunsubstituted methyl.

For instance, the passivating agent of the first aspect is often acompound of formula

wherein R⁹ and R¹⁰ are each independently a group selected from H andsubstituted or unsubstituted methyl or ethyl, optionally wherein two ormore of R⁹ and R¹⁰ are bonded together to form a ring. For instance, R⁹and R¹⁰ may be each independently a group selected from H andunsubstituted methyl or ethyl. Typically, R⁹ and R¹⁰ are eachindependently a group selected from H and unsubstituted methyl. Often,each R¹⁰ is H.

In one embodiment, the passivating compound is a hetrocyclic orheteroaryl compound comprising one or more nitrogen atoms. Examples ofhetrocyclic compounds comprising one or more N atoms include aziridine,azetidine, pyrrolidine, piperidine, azepane, morpholine, thiomorpholine,2H-pyrrole, 2-pyrroline, 3-pyrroline, 2-imidazoline, imidazolidine,2-pyrazoline, pyrazolidine, 3H-indole, indoline and quinuclidine.Examples of heteroaryl compound comprising one or more N atoms includepyrrole, oxazole, thiazole, imidazole, pyrazole, isoxazole, isothiazole,pyridine, pyridazine, pyrimidine, pyrazine, 1,3,5-triazine, indole,isoindole, benzimidazole, purine, quinoline, isoquinoline, carbazole,acridine and phenazine. Of these pyrrolidine, piperidine, morpholine,2H-pyrrole, 2-pyrroline, 3-pyrroline, pyrrole and pyridine arepreferred.

If the passivating agent is a heterocyclic or heteroaryl compoundcomprising one or more N atoms, it may be substituted or unsubstituted.For instance, it may be substituted with one or more substituted orunsubstituted C₁₋₆ alkyl groups. Often, the hetrocyclic or heteroarylpassivating agent is substituted with at most 2 unsubstituted C₁₋₃ alkylgroups.

A substituted or unsubstituted imine may be a compound of formulaR₂C═NR, wherein each R is independently selected from H and substitutedor unsubstituted C₁₋₁₈ alkyl (for instance C₁₋₆ alkyl) or substituted orunsubstituted aryl, optionally wherein the two R groups are bondedtogether to form a ring.

Often, the passivating agent of the first aspect is a substituted orunsubstituted pyridine. Thus, the passivating agent may be selected frompyridine, 2-methylpyridine, 3-methylpyridine, 2,6-dimethylpyridine,2,5-dimethylpyridine, 2-ethylpyridine, 3-ethylpyridine,2,6-diethylpyridine, 2,5-diethylpyridine, quinoline and acridine.

Substituted or unsubstituted pyrrolidines includes compounds of formula

wherein each R⁷ is independently a group selected from H andunsubstituted or substituted C₁₋₆-alkyl, optionally wherein two or moreR⁷ groups are bonded together to form a ring, and R⁸ is a group selectedfrom H and unsubstituted or substituted C₁₋₆-alkyl.

Preferably, each R⁷ is independently a group selected from H andunsubstituted or substituted C₁₋₃-alkyl, optionally wherein two or moreR⁷ groups are bonded together to form a ring, and R⁸ is a group selectedfrom H and unsubstituted or substituted C₁₋₃-alkyl. R⁸ is often H.

Substituted or unsubstituted pyrroles include compounds of formula

wherein each R⁷ is independently a group selected from H andunsubstituted or substituted C₁₋₆-alkyl, optionally wherein two or moreR⁷ groups are bonded together to form a ring, and R⁸ is a group selectedfrom H and unsubstituted or substituted C₁₋₆-alkyl.

Preferably, each R⁷ is independently a group selected from H andunsubstituted or substituted C₁₋₃-alkyl, optionally wherein two or moreR⁷ groups are bonded together to form a ring, and R⁸ is a group selectedfrom H and unsubstituted or substituted C₁₋₃-alkyl. R⁸ is often H.

The passivating agent of the first aspect may be an organic compoundcomprising one or more P atoms. Thus, the passivating compound may be asubstituted or unsubstituted phosphine. Examples of substituted orunsubstituted phosphines include compounds of formula PR₃, wherein eachR is independently a group selected H, unsubstituted or substitutedC₁₋₁₈-alkyl, unsubstituted or substituted C₃₋₁₀-cycloalkyl,unsubstituted or substituted C₂₋₁₈-alkenyl, unsubstituted or substitutedC₂₋₁₈-alkynyl, and unsubstituted or substituted aryl, and not all Rgroups are H, optionally wherein two or more of the R groups are bondedtogether to form a ring. Typically, each R is independently a groupselected from unsubstituted or substituted C₁₋₆-alkyl, unsubstituted orsubstituted C₃₋₆-cycloalkyl and unsubstituted or substituted aryl,optionally wherein two or more of the R groups are bonded together toform a ring. Thus, the passivating agent may be a triaryl phosphine, adiaryl alkyl phosphine, an aryl dialkyl phosphine or a trialkylphosphine. Preferably, each R is independently a group selected fromunsubstituted C₁₋₆-alkyl and unsubstituted or substituted aryl. Forinstance, the passivating agent may be triphenylphosphine,trimethylphosphine or tricyclohexylphosphine.

Preferably, the passivating agent of the first aspect is an organiccompound comprising one or more P or N atom selected from substitutedand unsubstituted pyridine, substituted and unsubstituted pyrrole,substituted and unsubstituted primary amines, substituted andunsubstituted secondary amines, substituted and unsubstituted tertiaryamines, and substituted and unsubstituted phosphines.

More preferably, the passivating agent of the first aspect is an organiccompound comprising one or more P or N atom which is a substituted andunsubstituted pyridine.

Most preferably, the passivating agent of the first aspect is pyridine(i.e. unsubstituted pyridine C₅H₅N).

In some instances, the passivating compound of the first aspect is not4-alkylpyridone, where alkyl is an alkyl group comprising 4 or morecarbon atoms. For instance, the passivating compound is often not4-tertbutylpyridine. The presence of bulky groups on the passivatingagent may introduce steric effects.

As described above, in the second aspect the passivating agent which isan organic compound is typically an organic compound comprisingnon-polar organic molecules. The molecules of the passivating agent donot chemically bond to anions or cations in the metal halide perovskite,but are disposed at/within the grain boundares and act to blockinteraction between anions and cations in adjacent grains of the metalhalide perovskite. The passivating agent may be a non-polar organiccompound such as a polycyclic aromatic hydrocarbon. By way of example,the passivating agent may comprise any of naphthelene, anthracene,phenanthrene, pyrene, and fluoranthene.

Metal Halide Perovskites

As mentioned above, in the first and second aspects of the invention thedevice may comprise a semiconductor, which semiconductor comprises: (a)a crystalline ionic solid; and (b) a passivating agent which is anorganic compound. The device may for instance comprise a semiconductor,which semiconductor comprises: (a) a crystalline ionic solid; and (b) apassivating agent which is an organic compound; wherein molecules of thepassivating agent are chemically bonded to anions or cations in thecrystalline ionic compound. When the semiconductor comprises acrystalline ionic solid, the crystalline ionic solid typically comprisesa metal oxide selected from TiO₂, SnO₂, ZnO, Nb₂O₅, Ta₂O₅, WO₃, W₂O₅,In₂O₃, Ga₂O₃, Nd₂O₃, PbO, and CdO. In particular, the metal oxide may beTiO₂. The crystalline ionic solid may comprise a semiconducting metalhalide or a semiconducting compound comprising copper. For instance, thecrystalline ionic solid may comprise CuI, CuBr, CuSCN, Cu₂O, CuO or CIS.Usually, however, the ionic compound is a metal halide perovskite, asdescribed hereinbelow.

Thus, the perovskite in the device of the invention is a metal halideperovskite. The formula of the metal halide perovskite comprises atleast one metal and at least one halide. The perovskite comprises afirst cation, a second cation and at least one halide anion, wherein atleast one of the first and second cations comprises a metal cation. Theperovskite may contain further cations and anions. The perovskite may bea layered perovskite.

Metal halide perovskites are described in WO 2013/171517, WO2013/171518, and WO 2013/171520, the entire contents of which areincorporated herein by reference. Any of the metal halide perovskitesdescribed in any of WO 2013/171517, WO 2013/171518, and WO 2013/171520may be used in the present invention.

The first cation may be any cation, but is often a metal cation or anorganic cation. If the first cation is a metal cation, it may be amonovalent or a divalent metal cation. The first cation may be selectedfrom Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺. The first cation is typically anorganic cation. If the first cation is an organic cation it may be anyorganic cation described below.

The second cation is typically a metal cation. The second cation may beany metal cation. The second cation may be a divalent metal cation. Thesecond cation may be a divalent metal cation selected from Ca²⁺, Sr²⁺,Cd²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Fe²⁺, Co²⁺, Pd²⁺, Ge²⁺, Sn²⁺, Pb²⁺, Sn²⁺, Yb²⁺and Eu²⁺.

Usually the at least one halide anion is selected from fluoride,chloride, bromide and iodide, for instance chloride, bromide and iodide.

The metal halide perovskite may be an organometal halide perovskite.Thus, the metal halide perovskite is typically a perovskite of theformula (I):

[A][B][X]₃  (I)

wherein:

-   -   [A] is at least one organic cation;    -   [B] is at least one metal cation, wherein [B] comprises at least        one of Ca²⁺, Sr²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Fe²⁺, Co²⁺, Pd²⁺,        Ge²⁺, Sn²⁺, Pb²⁺, Sn²⁺, Yb²⁺ and Eu²⁺; and    -   [X] is at least one halide anion.

The perovskite thus typically comprises an organic cation, a metalcation and at least halide anion. The metal halide perovskite may be aperovskite of the formula [A][B][X]₃ wherein:

[A] is at least one organic cation; [B] is at least one metal cationselected from Ca²⁺, Sr²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Fe²⁺, Co²⁺, Pd²⁺,Ge²⁺, Sn²⁺, Pb²⁺, Sn²⁺, Yb²⁺ and Eu²⁺; and [X] is at least one halideanion.[B] often comprises at least one of Sn²⁺, Pb²⁺, Cu²⁺, Ge²⁺ and Ni²⁺. Themetal cation may be selected from Sn²⁺, Pb²⁺, Cu²⁺, Ge²⁺ and Ni²⁺. Themetal cation may be selected from Sn²⁺ and Pb²⁺.

The organic cation may be any organic cation, i.e. a cation whichcomprises at least one carbon atom and optionally at least one hydrogenatom. The organic cation often has the formula (R⁵R⁶R⁷R⁸N)⁺, wherein: R⁵is a group selected from H, unsubstituted or substituted C₁₋₁₈-alkyl,unsubstituted or substituted C₃₋₁₀-cycloalkyl, unsubstituted orsubstituted C₂₋₁₈-alkenyl, unsubstituted or substituted C₂₋₁₈-alkynyl,and unsubstituted or substituted aryl; R⁶ is a group selected from H,unsubstituted or substituted C₁₋₁₈-alkyl, unsubstituted or substitutedC₃₋₁₀-cycloalkyl, unsubstituted or substituted C₂₋₁₈-alkenyl,unsubstituted or substituted C₂₋₁₈-alkynyl, and unsubstituted orsubstituted aryl; R⁷ is a group selected from H, unsubstituted orsubstituted C₁₋₁₈-alkyl, unsubstituted or substituted C₃₋₁₀-cycloalkyl,unsubstituted or substituted C₂₋₁₈-alkenyl, unsubstituted or substitutedC₂₋₁₈-alkynyl, and unsubstituted or substituted aryl; and R⁸ is a groupselected from H, unsubstituted or substituted C₁₋₁₈-alkyl, unsubstitutedor substituted C₃₋₁₀-cycloalkyl, unsubstituted or substitutedC₂₋₁₈-alkenyl, unsubstituted or substituted C₂₋₁₈-alkynyl, andunsubstituted or substituted aryl.

The organic cation may have the formula (R⁵R⁶R⁷R⁸N)⁺, wherein: R⁵ is agroup selected from H, unsubstituted C₁₋₁₈-alkyl, and unsubstitutedaryl; R⁶ is a group selected from H, unsubstituted C₁₋₁₈-alkyl, andunsubstituted aryl; R⁷ is a group selected from H, unsubstitutedC₁₋₁₈-alkyl, and unsubstituted aryl; and R⁸ is a group selected from H,unsubstituted C₁₋₁₈-alkyl, and unsubstituted aryl.

For instance, the organic cation may have the formula (R⁹NH₃)⁺, wherein:R⁹ is hydrogen, or unsubstituted or substituted C₁₋₁₈-alkyl. Forinstance, R⁹ may be methyl or ethyl. Typically, R⁹ is methyl.

The organic cation may have the formula (R⁵R⁶N═CH—NR⁷R⁸)⁺, wherein: R⁵is a group selected from H, unsubstituted or substituted C₁₋₁₈-alkyl,unsubstituted or substituted C₃₋₁₀-cycloalkyl, unsubstituted orsubstituted C₂₋₁₈-alkenyl, unsubstituted or substituted C₂₋₁₈-alkynyl,and unsubstituted or substituted aryl; R⁶ is a group selected from H,unsubstituted or substituted C₁₋₁₈-alkyl, unsubstituted or substitutedC₃₋₁₀-cycloalkyl, unsubstituted or substituted C₂₋₁₈-alkenyl,unsubstituted or substituted C₂₋₁₈-alkynyl, and unsubstituted orsubstituted aryl; R⁷ is a group selected from H, unsubstituted orsubstituted C₁₋₁₈-alkyl, unsubstituted or substituted C₃₋₁₀-cycloalkyl,unsubstituted or substituted C₂₋₁₈-alkenyl, unsubstituted or substitutedC₂₋₁₈-alkynyl, and unsubstituted or substituted aryl; and R⁸ is a groupselected from H, unsubstituted or substituted C₁₋₁₈-alkyl, unsubstitutedor substituted C₃₋₁₀-cycloalkyl, unsubstituted or substitutedC₂₋₁₈-alkenyl, unsubstituted or substituted C₂₋₁₈-alkynyl, andunsubstituted or substituted aryl.

The organic cation may have the formula (R⁵R⁶N═CH—NR⁷R⁸)⁺, wherein: R⁵is a group selected from H, unsubstituted C₁₋₁₈-alkyl, and unsubstitutedaryl; R⁶ is a group selected from H, unsubstituted C₁₋₁₈-alkyl, andunsubstituted aryl; R⁷ is a group selected from H, unsubstitutedC₁₋₁₈-alkyl, and unsubstituted aryl; and R⁸ is a group selected from H,unsubstituted C₁₋₁₈-alkyl, and unsubstituted aryl.

Typically, R⁵ in the cation (R⁵R⁶N═CH—NR⁷R⁸)⁺ is hydrogen, methyl orethyl, R⁶ is hydrogen, methyl or ethyl, R⁷ is hydrogen, methyl or ethyl,and R⁸ is hydrogen, methyl or ethyl. For instance R⁵ may be hydrogen ormethyl, R⁶ may be hydrogen or methyl, R⁷ may be hydrogen or methyl, andR⁸ may be hydrogen or methyl. The organic cation may, for example, havethe formula (H₂N═CH—NH₂)⁺.

The perovskite may be a mixed-halide perovskite, wherein the at leastone halide anion may be two or more different halide anions. They may betwo or three halide anions, or more typically, two different halideanions. Usually the halide anions are selected from fluoride, chloride,bromide and iodide, for instance chloride, bromide and iodide.

The perovskite of formula (I) may comprise one, two, three or fourdifferent metal cations, typically one or two different metal cations.Also, the perovskite of the formula (I), may, for instance, compriseone, two, three or four different organic cations, typically one or twodifferent organic cations. Likewise, the perovskite of formula (I), may,comprise one two, three or four different anions, typically two or threedifferent anions.

The organic and metal cations in the perovskite compound of formula (I)may be as further defined hereinbefore. Thus the organic cations may beselected from cations of formula (R⁵R⁶R⁷R⁸N)⁺, cations of formula(R⁹NH3)⁺, and cations of formula (R⁵R⁶N═CH—NR⁷R⁸)⁺ as defined above. Themetal cations may be selected from divalent metal cations. For instance,the metal cations may be selected from Ca²⁺, Sr²⁺, Cd²⁺, Cu²⁺, Ni²⁺,Mn²⁺, Fe²⁺, Co²⁺, Pd²⁺, Ge²⁺, Sn²⁺, Pb²⁺, Yb²⁺ and Eu²⁺. The metalcation may be selected from Sn²⁺, Pb²⁺, Cu²⁺, Ge²⁺ and Ni²⁺. The metalcation may be Sn²⁺ or Pb²⁺.

In one embodiment, the perovskite is a perovskite compound of theformula (IA):

AB[X]₃  (IA)

wherein: A is an organic cation; B is a metal cation; and [X] is two ormore different halide anions. Preferably, [X] is two or three differenthalide anions. More preferably, [X] is two different halide anions. Theorganic cation and metal cation may be as defined above.

The metal halide perovskite is a perovskite compound of formula (II):

ABX_(3-x)X′_(x)  (II)

wherein: A is an organic cation; B is a metal cation; X is a firsthalide anion; X′ is a second halide anion which is different from thefirst halide anion; and x is from 0 to 3. Usually, x is from 0.05 to0.95. For instance, x may be from 0.5 to 2.5, or from 0.75 to 2.25.Typically, x is from 1 to 2.

Again, in formula (II), the organic and metal cations may be as furtherdefined hereinbefore. Thus the organic cations may be selected fromcations of formula (R⁵R⁶R⁷R⁸N)⁺, cations of formula (R⁹NH3)⁺, andcations of formula (R⁵R⁶N═CH—NR⁷R⁸)⁺ as defined above. The metal cationsmay be selected from divalent metal cations. For instance, the metalcations may be selected from Ca²⁺, Sr²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Fe²⁺,Co²⁺, Pd²⁺, Ge²⁺, Sn²⁺, Pb²⁺, Yb²⁺ and Eu²⁺. The metal cation may beselected from Sn²⁺, Pb²⁺, Cu²⁺, Ge²⁺ and Ni²⁺. The metal cation may beSn²⁺ or Pb²⁺.

The metal halide perovskite may be a perovskite compound selected fromCH₃NH₃PbI₃, CH₃NH₃PbBr₃, CH₃NH₃PbCl₃, CH₃NH₃PbF₃, CH₃NH₃PbBr_(x)I_(3-x),CH₃NH₃PbBr_(x)Cl_(3-x), CH₃NH₃PbI_(x)Br_(3-x), CH₃NH₃PbI_(x)Cl_(3-x),CH₃NH₃PbCl_(x)Br_(3-x), CH₃NH₃PbI_(3-x)Cl_(x), CH₃NH₃SnI₃, CH₃NH₃SnBr₃,CH₃NH₃SnCl₃, CH₃NH₃SnF₃, CH₃NH₃SnBrI₂, CH₃NH₃SnBr_(x)I_(3-x),CH₃NH₃SnBr_(x)Cl_(3-x), CH₃NH₃SnF_(3-x)Br_(x), CH₃NH₃SnI_(x)Br_(3-x),CH₃NH₃SnI_(x)Cl_(3-x), CH₃NH₃SnF_(3-x)I_(x), CH₃NH₃SnCl_(x)Br_(3-x),CH₃NH₃SnI_(3-x)Cl_(x) and CH₃NH₃SnF_(3-x)Cl_(x), where x is from 0 to 3.x may be from 0.05 to 2.96. For instance, x may be from 0.1 to 2.9, orfrom 0.5 to 2.5. In some cases, x is from 0.75 to 2.25, or from 1 to 2.

The metal halide perovskite may be a perovskite compound selected fromCH₃NH₃PbI₃, CH₃NH₃PbBr₃, CH₃NH₃PbCl₃, CH₃NH₃PbF₃, CH₃NH₃PbBrI₂,CH₃NH₃PbBrCl₂, CH₃NH₃PbIBr₂, CH₃NH₃PbICl₂, CH₃NH₃PbClBr₂, CH₃NH₃PbI₂Cl,CH₃NH₃SnI₃, CH₃NH₃SnBr₃, CH₃NH₃SnCl₃, CH₃NH₃SnF₃, CH₃NH₃SnBr₂,CH₃NH₃SnBrCl₂, CH₃NH₃SnF₂Br, CH₃NH₃SnIBr₂, CH₃NH₃SnICl₂, CH₃NH₃SnF₂I,CH₃NH₃SnClBr₂, CH₃NH₃SnI₂Cl and CH₃NH₃SnF₂Cl.

The metal halide perovskite may be a perovskite compound selected fromCH₃NH₃PbBr_(x)I_(3-x), CH₃NH₃PbBr_(x)Cl_(3-x), CH₃NH₃PbI_(x)Br_(3-x),CH₃NH₃PbI_(x)Cl_(3-x), CH₃NH₃PbCl_(x)Br_(3-x), CH₃NH₃PbI_(3-x)Cl_(x),CH₃NH₃SnBr_(x)I_(3-x), CH₃NH₃SnBr_(x)Cl_(3-x), CH₃NH₃SnF_(3-x)Br_(x),CH₃NH₃SnI_(x)Br_(3-x), CH₃NH₃SnI_(x)Cl_(3-x), CH₃NH₃SnF_(3-x)I_(x),CH₃NH₃SnCl_(x)Br_(3-x), CH₃NH₃SnI_(3-x)Cl_(x) and CH₃NH₃SnF_(3-x)Cl_(x),where x is from 0.05 to 2.95. For instance, x may be from 0.5 to 2.5,from 0.75 to 2.25, or from 1 to 2.

The perovskites may be selected from CH₃NH₃PbBrI₂, CH₃NH₃PbBrCl₂,CH₃NH₃PbIBr₂, CH₃NH₃PbICl₂, CH₃NH₃PbClBr₂, CH₃NH₃PbI₂Cl, CH₃NH₃SnBrI₂,CH₃NH₃SnBrCl₂, CH₃NH₃SnF₂Br, CH₃NH₃SnIBr₂, CH₃NH₃SnICl₂, CH₃NH₃SnF₂I,CH₃NH₃SnClBr₂, CH₃NH₃SnI₂Cl and CH₃NH₃SnF₂Cl.

The perovskite may be selected from CH₃NH₃PbBrI₂, CH₃NH₃PbBrCl₂,CH₃NH₃PbIBr₂, CH₃NH₃PbICl₂, CH₃NH₃PbClBr₂, CH₃NH₃PbI₂Cl, CH₃NH₃SnF₂Br,CH₃NH₃SnICl₂, CH₃NH₃SnF₂I, CH₃NH₃SnI₂Cl and CH₃NH₃SnF₂Cl.

The perovskite may be selected from CH₃NH₃PbBrI₂, CH₃NH₃PbBrCl₂,CH₃NH₃PbIBr₂, CH₃NH₃PbICl₂, CH₃NH₃PbClBr₂, CH₃NH₃PbI₂Cl, CH₃NH₃SnF₂Br,CH₃NH₃SnF₂I and CH₃NH₃SnF₂Cl.

The perovskite may be selected from CH₃NH₃PbBrI₂, CH₃NH₃PbBrCl₂,CH₃NH₃PbIBr₂, CH₃NH₃PbICl₂, CH₃NH₃SnF₂Br, and CH₃NH₃SnF₂I. Theperovskite may be CH₃NH₃PbCl₂I.

As mentioned above, passivation as described herein may be used tostabilize some organometal perovskites. Thus, the metal halideperovskite may be any metal halide perovskite described herein, whereinthe metal cation is Ge²⁺ or Cu⁺². For instance, the metal halideperovskite may be selected from CH₃NH₃PbI₃, CH₃NH₃PbBr₃, CH₃NH₃PbCl₃,CH₃NH₃PbF₃, CH₃NH₃PbBr_(x)I_(3-x), CH₃NH₃PbBr_(x)Cl_(3-x),CH₃NH₃PbI_(x)Br_(3-x), CH₃NH₃PbI_(x)Cl_(3-x), CH₃NH₃PbCl_(x)Br_(3-x),CH₃NH₃PbI_(3-x)Cl_(x), CH₃NH₃SnI₃, CH₃NH₃SnBr₃, CH₃NH₃SnCl₃, CH₃NH₃SnF₃,CH₃NH₃SnBr₂, CH₃NH₃SnBr_(x)I_(3-x), CH₃NH₃SnBr_(x)Cl_(3-x),CH₃NH₃SnF_(3-x)Br_(x), CH₃NH₃SnI_(x)Br_(3-x), CH₃NH₃SnICl_(3-x),CH₃NH₃SnF_(3-x)I_(x), CH₃NH₃SnCl_(x)Br_(3-x), CH₃NH₃SnI_(3-x)Cl_(x), andCH₃NH₃SnF_(3-x), Cl_(x)CH₃NH₃CuI₃, CH₃NH₃CuBr₃, CH₃NH₃CuCl₃, CH₃NH₃CuF₃,CH₃NH₃CuBrI₂, CH₃NH₃CuBr_(x)I_(3-x), CH₃NH₃CuBr_(x)Cl_(3-x),CH₃NH₃CuF_(3-x)Br_(x), CH₃NH₃CuI_(x)Br_(3-x), CH₃NH₃CuI_(x)Cl_(3-x),CH₃NH₃CuF_(3-x)I_(x), CH₃NH₃CuCl_(x)Br_(3-x), CH₃NH₃CuI_(3-x)Cl_(x) andCH₃NH₃CuF_(3-x)Cl_(x), Cl_(x)CH₃NH₃GeI₃, CH₃NH₃GeBr₃, CH₃NH₃GeCl₃,CH₃NH₃GeF₃, CH₃NH₃GeBrI₂, CH₃NH₃GeBr_(x)I_(3-x), CH₃NH₃GeBr_(x)Cl_(3-x),CH₃NH₃GeF_(3-x)Br_(x), CH₃NH₃GeI_(x)Br_(3-x), CH₃NH₃GeI_(x)Cl_(3-x),CH₃NH₃GeF_(3-x)I_(x), CH₃NH₃GeCl_(x)Br_(3-x), CH₃NH₃GeI_(3-x)Cl_(x) andCH₃NH₃GeF_(3-x)Cl where x is from 0 to 3. x may be from 0.05 to 2.96.For instance, x may be from 0.1 to 2.9, or from 0.5 to 2.5. In somecases, x is from 0.75 to 2.25, or from 1 to 2.

The perovskite employed in the devices of the invention may comprise amixed-halide perovskite and a single-halide perovskite, for instance ina blend, wherein said single-halide perovskite comprises a first cation,a second cation and a halide anion; wherein the first and second cationsare as hereinbefore defined. For instance, the optoelectronic device maycomprise: CH₃NH₃PbICl₂ and CH₃NH₃PbI₃; CH₃NH₃PbICl₂ and CH₃NH₃PbBr₃;CH₃NH₃PbBrCl₂ and CH₃NH₃PbI₃; or CH₃NH₃PbBrCl₂ and CH₃NH₃PbBr₃.

Alternatively, semiconductor employed in the device of the invention maycomprise more than one metal halide perovskite, wherein each perovskiteis a mixed-halide perovskite, and wherein said mixed-halide perovskiteis as herein defined. For instance, the semiconductor may comprise twoor three said perovskites. The semiconductor may, for instance, comprisetwo perovskites wherein both perovskites are mixed-anion perovskites.For instance, the optoelectronic device may comprise: CH₃NH₃PbICl₂ andCH₃NH₃PbIBr₂; CH₃NH₃PbICl₂ and CH₃NH₃PbBrI₂; CH₃NH₃PbBrCl₂ andCH₃NH₃PbIBr₂; or CH₃NH₃PbBrCl₂ and CH₃NH₃PbIBr₂.

When [B] is a single metal cation which is Pb²⁺, one of said two or moredifferent halide anions may be iodide or fluoride; and when [B] is asingle metal cation which is Sn²⁺ one of said two or more differenthalide anions may be fluoride. One of said two or more different halideanions may be iodide or fluoride. One of said two or more differenthalide anions may be iodide and another of said two or more differenthalide anions may be fluoride or chloride. One of said two or moredifferent halide anions may be fluoride. One of said two or moredifferent anions may be fluoride and another of said two or moredifferent anions may be chloride, bromide or iodide. One of said two ormore different anions may be iodide and another of said two or moredifferent anions may be fluoride or chloride. [X] may be two differenthalide anions X and X′. Said divalent metal cation may be Sn²⁺. Saiddivalent metal cation may be Pb²⁺.

The metal halide perovskite may be doped. For instance, the metal halideperovskite may be doped by the introduction of an impurity atom. Forinstance, the metal halide perovskite could be doped with a metalimpurity of a different charge from the other metals in the perovskite.Thus, the perovskite could further comprise metal dopant selected frommetals with an oxidation state of IV, III or I, for instance bismuth(III), antimony (III), tin (IV) or thallium (I).

The metal halide perovskite employed in the device of the inventionpreferably has a band gap which is narrow enough to allow the excitationof electrons by incident light. A band gap of 3.0 eV or less isparticularly preferred, especially when the device is a photovoltaicdevice, because such a band gap is low enough for sunlight to exciteelectrons across it.

Accordingly, the metal halide perovskite employed in device of theinvention typically has a band gap of equal to or less than 3.0 eV. Insome embodiments, the band gap of the perovskite is less than or equalto 2.8 eV, for instance equal to or less than 2.5 eV. The band gap mayfor instance be less than or equal to 2.3 eV, or for instance less thanor equal to 2.0 eV.

Usually, the band gap is at least 0.5 eV. Thus, the band gap of theperovskite may be from 0.5 eV to 2.8 eV. In some embodiments it is from0.5 eV to 2.5 eV, or for example from 0.5 eV to 2.3 eV. The band gap ofthe perovskite may for instance be from 0.5 eV to 2.0 eV. In otherembodiments, the band gap of the perovskite may be from 1.0 eV to 3.0eV, or for instance from 1.0 eV to 2.8 eV. In some embodiments it isfrom 1.0 eV to 2.5 eV, or for example from 1.0 eV to 2.3 eV. The bandgap of the metal perovskite may for instance be from 1.0 eV to 2.0 eV.

The metal halide perovskite may have a band gap of less than or equal to3.0 eV. The metal halide perovskite may have a band gap of less than orequal to 2.0 eV.

Device

The invention also provides a device comprising a semiconductor, whichsemiconductor comprises: (a) a metal halide perovskite; and (b) apassivating agent which is (i) a halogen bond donor compound, or (ii) anorganic compound comprising at least one thiol or sulfide group.

This device may be as further defined anywhere hereinbefore. Thepassivating agent may be as defined hereinbefore, and/or the metalhalide perovskite may be as defined hereinbefore.

Layers of Passivated Perovskite

In many devices according to the invention, the passivated perovskitewill be in the form of a layer. Thus, in one embodiment, the devicecomprises a layer of said semiconductor. The device may comprise a layerof the metal halide perovskite. The layer of the semiconductor comprisesthe passivating agent and the metal halide perovskite.

According to the first aspect, the device will comprise: (a) a layer ofa metal halide perovskite; and (b) a passivating agent which is anorganic compound; wherein molecules of the passivating agent arechemically bonded to anions or cations in the metal halide perovskite.Molecules of the passivating agent will typically be bonded to anions orcations in the mixed halide by supramolecular chemical bonds, asdescribed above.

According to the second aspect, the device will comprise: (a) a layer ofa metal halide perovskite; and (b) a passivating agent which is anorganic compound; wherein molecules of the passivating agent aredisposed at grain boundaries within the metal halide perovskite and arenot chemically bonded to anions or cations in the metal halideperovskite. Molecules of the passivating agent block interaction betweenanions and cations in adjacent grains of the metal halide perovskite atthe grain boundaries.

The devices may comprise a layer of the semiconductor, wherein the layerof the semiconductor is without open porosity. The layer of thesemiconductor may comprise a layer of the metal halide perovskite, whichlayer of the metal halide perovskite is without open porosity.Alternatively, the layer of the semiconductor may be porous, or thelayer of the semiconductor may be deposited on a porous scaffold.Non-porous layers of the semiconductor may be used in devices whichrequire a planar heterojunction between the perovskite and any othermaterials in the device, for instance n- or p-type regions. Porouslayers of the semiconductor, or layers of the semiconductor deposited ona porous scaffold, may be used in devices which require large surfaceareas or a bulk heterojunction, for instance perovskite sensitizeddevices (such as those described in WO 2013/171518 and WO 2013/171520).

If the layer of the semiconductor is without open porosity, it may be a“capping layer”, which is a layer of the semiconductor which is disposedon a first layer which comprises a scaffold material and the metalhalide perovskite. In this case, the capping layer is not infiltrated bythe scaffold material, because the capping layer and the perovskitesemiconductor within the capping layer are without open porosity. Themetal perovskite in the first layer, on the other hand (which isgenerally the same perovskite compound as the perovskite compound in thecapping layer), is typically disposed in pores of the scaffold materialand may therefore be said to be “infiltrated” by the scaffold material.

The scaffold material referred to herein may be a dielectric scaffoldmaterial or an n-type scaffold material. A dielectric scaffold materialmay comprise a material having a band gap greater than or equal to 3.6eV, or greater than or equal to 4 eV. A dielectric scaffold material maybe selected from a dielectric oxide. A dielectric scaffold may beselected from alumina and silica, for instance alumina (Al₂O₃). Ann-type scaffold may be selected from any n-type material describedherein, for instance titania (TiO₂).

In some embodiments of the optoelectronic devices of the presentinvention, the layer of the semiconductor without open porosity isnon-porous.

Generally, a layer of the semiconductor without open porosity mayconsist essentially of the perovskite and the passivating agent. Aperovskite is a crystalline compound. Thus, the layer of thesemiconductor without open porosity may consist essentially ofcrystallites/grains of the perovskite together with the passivatingagent. The layer of the semiconductor without open porosity may consistof a layer of the metal halide perovskite without open porosity and thepassivating agent. Thus, a layer of the semiconductor without openporosity may consist of crystallites of the perovskite and thepassivating agent.

The device of the invention may be a thin film device.

Usually, the thickness of the layer of the metal halide perovskite orthe semiconductor is from 10 nm to 100 μm. The thickness of the layer ofthe semiconductor may be from 10 nm to 10 μm. Preferably, the thicknessof the layer of the semiconductor is from 50 nm to 1000 nm, for instancefrom 100 nm to 2000 nm, from 100 nm to 1000 nm, or from 100 nm to 700nm. The thickness of the layer of the semiconductor is often greaterthan 100 nm. The thickness may, for example, be from 100 nm to 100 μm,or for instance from 100 nm to 700 nm. These thicknesses may apply tothe layer of the semiconductor when the device comprises a layer of thesemiconductor without open porosity. For instance, the device maycomprise a layer of the semiconductor, which layer is without openporosity and has a thickness of from 50 nm to 1000 nm, or of greaterthan or equal to 100 nm.

Device Structure

The devices according to the invention may comprise:

-   -   (a) an n-type region comprising at least one n-type layer;    -   (b) a p-type region comprising at least one p-type layer; and,        disposed between the n-type region and the p-type region:    -   (c) a layer of the semiconductor.

The devices may comprise: (a) an n-type region comprising at least onen-type layer; (b) a p-type region comprising at least one p-type layer;and, disposed between the n-type region and the p-type region: (c) alayer of the semiconductor comprising the metal halide perovskite andthe passivating agent; wherein the layer of a semiconductor comprises alayer of the metal halide perovskite as defined anywhere hereinbefore.The metal halide perovskite may be defined as anywhere hereinbefore. Thepassivating agent may be as defined anywhere hereinbefore.

Optoelectronic devices comprising metal halide perovskites are describedin WO 2013/171517, WO 2013/171518, and WO 2013/171520, the contents ofwhich are incorporated by reference herein in their entirety. The deviceaccording to the present invention may have a structure as described inany of WO 2013/171517, WO 2013/171518, and WO 2013/171520.

The layer of the semiconductor may comprise a layer of the metal halideperovskite, which layer of metal halide perovskite is without openporosity. The layer of the semiconductor may be without open porosity.In this case, the layer of the semiconductor is not thereforeinfiltrated by the, or any of the, n-type material(s) in the n-typeregion, and likewise it is not infiltrated by the, or any of the, p-typematerial(s) in the p-type region. Rather, the layer of the semiconductorwithout open porosity typically forms a planar heterojunction with then-type or the p-type region, or in some cases it forms planar aheterojunction with both the n-type region and the p-type region. Whenthe layer of the semiconductor forms a planar heterojunction with then-type region and/or p-type region, the passivating agent may be presentat the heterojunction. As the passivating agent may form a monolayer ona surface of the perovskite, this monolayer may lie along theheterojunction. In addition, when the layer of the semiconductor forms aplanar heterojunction with the n-type region and/or p-type region, thepassivating agent may be present at grain boundaries within theperovskite.

The layer of a semiconductor comprising the metal halide perovskite andthe passivating agent may comprise a porous layer of the metal halideperovskite. Thus, the layer of the semiconductor may be porous. Thelayer of a semiconductor comprising the metal halide perovskite and thepassivating agent may comprise a layer of the metal halide perovskitedisposed on a porous scaffold.

The n-type region in the devices may comprise one or more n-type layers.Often, the n-type region is an n-type layer, i.e. a single n-type layer.An n-type layer is a layer of an electron-transporting (i.e. an n-type)material. The n-type material may be a single n-type compound orelemental material, or a mixture of two or more n-type compounds orelemental materials, which may be undoped or doped with one or moredopant elements. The n-type layer employed in the device may comprise aninorganic or an organic n-type material.

A suitable inorganic n-type material may be selected from a metal oxide,a metal sulphide, a metal selenide, a metal telluride, a perovskite,amorphous Si, an n-type group IV semiconductor, an n-type group III-Vsemiconductor, an n-type group II-VI semiconductor, an n-type groupI-VII semiconductor, an n-type group IV-VI semiconductor, an n-typegroup V-VI semiconductor, and an n-type group II-V semiconductor, any ofwhich may be doped or undoped. More typically, the n-type material isselected from a metal oxide, a metal sulphide, a metal selenide, and ametal telluride. The n-type layer may comprise an inorganic materialselected from oxide of titanium, tin, zinc, niobium, tantalum, tungsten,indium, gallium, neodinium, palladium, or cadmium, or an oxide of amixture of two or more of said metals. For instance, the n-type layermay comprise TiO₂, SnO₂, ZnO, Nb₂O₅, Ta₂O₅, WO₃, W₂O₅, In₂O₃, Ga₂O₃,Nd₂O₃, PbO, or CdO. Other suitable n-type materials that may be employedinclude sulphides of cadmium, tin, copper, or zinc, including sulphidesof a mixture of two or more of said metals. For instance, the sulphidemay be FeS₂, CdS, ZnS or Cu₂ZnSnS₄. The n-type layer may for instancecomprise a selenide of cadmium, zinc, indium, or gallium or a selenideof a mixture of two or more of said metals; or a telluride of cadmium,zinc, cadmium or tin, or a telluride of a mixture of two or more of saidmetals. For instance, the selenide may be Cu(In,Ga)Se₂. Typically, thetelluride is a telluride of cadmium, zinc, cadmium or tin. For instance,the telluride may be CdTe. The n-type layer may for instance comprise aninorganic material selected from oxide of titanium, tin, zinc, niobium,tantalum, tungsten, indium, gallium, neodinium, palladium, cadmium, oran oxide of a mixture of two or more of said metals; a sulphide ofcadmium, tin, copper, zinc or a sulphide of a mixture of two or more ofsaid metals; a selenide of cadmium, zinc, indium, gallium or a selenideof a mixture of two or more of said metals; or a telluride of cadmium,zinc, cadmium or tin, or a telluride of a mixture of two or more of saidmetals. Examples of other semiconductors that may be suitable n-typematerials, for instance if they are n-doped, include group IV compoundsemiconductors; amorphous Si; group III-V semiconductors (e.g. galliumarsenide); group II-VI semiconductors (e.g. cadmium selenide); groupI-VII semiconductors (e.g. cuprous chloride); group IV-VI semiconductors(e.g. lead selenide); group V-VI semiconductors (e.g. bismuthtelluride); and group II-V semiconductors (e.g. cadmium arsenide).Typically, the n-type layer comprises TiO₂. When the n-type layer is aninorganic material, for instance TiO₂ or any of the other materialslisted above, it may be a compact layer of said inorganic material.Preferably the n-type layer is a compact layer of TiO₂.

The p-type region in the devices may comprise one or more p-type layers.Often, the p-type region is a p-type layer, i.e. a single p-type layer.A p-type layer is a layer of a hole-transporting (i.e. a p-type)material. The p-type material may be a single p-type compound orelemental material, or a mixture of two or more p-type compounds orelemental materials, which may be undoped or doped with one or moredopant elements. The p-type layer may comprise an inorganic or anorganic p-type material. Suitable p-type materials may be selected frompolymeric or molecular hole transporters.

The p-type layer employed may, for instance, comprise spiro-OMeTAD(2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)9,9′-spirobifluorene)),P3HT (poly(3-hexylthiophene)), PCPDTBT(Poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl]]),or PVK (poly(N-vinylcarbazole)). Usually, the p-type material isselected from spiro-OMeTAD, P3HT, PCPDTBT and PVK. Preferably, thep-type layer comprises spiro-OMeTAD. Suitable p-type materials alsoinclude molecular hole transporters, polymeric hole transporters andcopolymer hole transporters. The p-type material may, for instance, be amolecular hole transporting material, a polymer or copolymer comprisingone or more of the following moieties: thiophenyl, phenelenyl,dithiazolyl, benzothiazolyl, diketopyrrolopyrrolyl, ethoxydithiophenyl,amino, triphenyl amino, carbozolyl, ethylene dioxythiophenyl,dioxythiophenyl, or fluorenyl. Suitable p-type materials also includem-MTDATA (4,4′,4″-tris(methylphenylphenylamino)triphenylamine), MeOTPD(N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine), BP2T(5,5′-di(biphenyl-4-yl)-2,2′-bithiophene), Di-NPB(N,N′-Di-[(1-naphthyl)-N,N′-diphenyl]-1,1′-biphenyl)-4,4′-diamine),α-NPB (N,N′-di(naphthalen-1-yl)-N,N′-diphenyl-benzidine), TNATA(4,4′,4″-tris-(N-(naphthylen-2-yl)-N-phenylamine)triphenylamine), BPAPF(9,9-bis[4-(N,N-bis-biphenyl-4-yl-amino)phenyl]-9H-fluorene), spiro-NPB(N2,N7-Di-1-naphthalenyl-N2,N7-diphenyl-9,9′-spirobi[9H-fluorene]-2,7-diamine),4P-TPD (4,4′-bis-(N,N-diphenylamino)-tetraphenyl), PEDOT:PSS andspiro-OMeTAD. The p-type layer may be doped with an ionic salt or abase. The p-type layer may for instance be doped with an ionic saltselected from HMI-TFSI (1-hexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide) and Li-TFSI (lithiumbis(trifluoromethanesulfonyl)imide), or with a base which is tBP(tert-butylpyridine). Additionally or alternatively, the p-type layermay be doped to increase the hole-density. The p-type layer may forinstance be doped with NOBF₄ (Nitrosonium tetrafluoroborate), toincrease the hole-density. The p-type layer may comprise an inorganichole transporter. For instance, the p-type layer may comprise aninorganic hole transporter comprising an oxide of nickel, vanadium,copper or molybdenum; CuI, CuBr, CuSCN, Cu₂O, CuO or CIS; a perovskite;amorphous Si; a p-type group IV semiconductor, a p-type group III-Vsemiconductor, a p-type group II-VI semiconductor, a p-type group I-VIIsemiconductor, a p-type group IV-VI semiconductor, a p-type group V-VIsemiconductor, and a p-type group II-V semiconductor, which inorganicmaterial may be doped or undoped. The p-type layer may be a compactlayer of said inorganic hole transporter. The p-type layer may forinstance comprise an inorganic hole transporter comprising an oxide ofnickel, vanadium, copper or molybdenum; CuI, CuBr, CuSCN, Cu₂O, CuO orCIS; amorphous Si; a p-type group IV semiconductor, a p-type group III-Vsemiconductor, a p-type group II-VI semiconductor, a p-type group I-VIIsemiconductor, a p-type group IV-VI semiconductor, a p-type group V-VIsemiconductor, and a p-type group II-V semiconductor, which inorganicmaterial may be doped or undoped. The p-type layer may for instancecomprise an inorganic hole transporter selected from CuI, CuBr, CuSCN,Cu₂O, CuO and CIS. The p-type layer may be a compact layer of saidinorganic hole transporter.

Typically, the p-type layer comprises a polymeric or molecular holetransporter, and the n-type layer comprises an inorganic n-typematerial. The p-type polymeric or molecular hole transporter may be anysuitable polymeric or molecular hole transporter, for instance any ofthose listed above. Likewise, the inorganic n-type material may be anysuitable n-type inorganic, for instance any of those listed above. Inone embodiment, for instance, the p-type layer comprises spiro-OMeTADand the n-type layer comprises TiO₂. Typically, in that embodiment, then-type layer which comprises TiO₂ is a compact layer of TiO₂.

Types of Devices

A device of the present invention may be any device comprising a metalhalide perovskite and a passivating agent which is an organic compound.For instance, the device may be an optoelectronic device, e.g. aphotovoltaic device; a transistor; or a diode.

Generally, a device of the present invention is a semiconductor device,or a semiconducting device. The terms “semiconductor device” and“semiconducting device”, as used herein, are interchangeable, and referto a device, a functional component of which comprises a semiconductor.

A device of the present invention may for instance be an optoelectronicdevice. The optoelectronic device may be selected from a photovoltaicdevice; a photo resistor; a light-sensitive detector; solid-statetriode; a battery electrode; a light emitting device; a light emittingdiode; a transistor; a solar cell; a laser; or a diode injection laser.Typically, the optoelectronic device is a photovoltaic device.

When a device of the invention is a photovoltaic device, thephotovoltaic device may be selected from a photodiode, a solar cell, aphotodetector, and a photosensor. The photovoltaic device is typically asolar cell. When the device is a photovoltaic device, the photovoltaicdevice may have the structure described above, i.e. it may comprise (a)an n-type region comprising at least one n-type layer; (b) a p-typeregion comprising at least one p-type layer; and, disposed between then-type region and the p-type region: (c) a layer of a semiconductorcomprising the metal halide perovskite and the passivating agent. In aphotovoltaic device according to the invention, the semiconductor asdescribed herein is typically the main light-absorbing semiconductor.

The optoelectronic device may alternatively be an optoelectronic deviceother than a photovoltaic device. The optoelectronic device may forinstance be selected from a light emitting device, a light emittingdiode, a laser, and a transistor. The optoelectronic device may beselected from a light emitting device, a light emitting diode, anoptically pumped laser, an electrical injection laser, and a transistor.

In one embodiment, the device is a light emitting device. It may forinstance be a light emitting diode, or a charge injection laser diode.

In another embodiment, the device is a transistor.

Usually, however, the device is a photovoltaic device.

Process for Producing a Device

In accordance with the first aspect, the invention provides a processfor producing a device comprising a semiconductor, which semiconductorcomprises:

-   -   (a) a metal halide perovskite; and    -   (b) a passivating agent which is an organic compound;    -   wherein molecules of the passivating agent are chemically bonded        to anions or cations in the metal halide perovskite,    -   wherein the process comprises treating a metal halide perovskite        with a passivating agent, which passivating agent is an organic        compound and is suitable for chemically bonding to anions or        cations in the metal halide perovskite.

In accordance with the second aspect, the invention provides a processfor producing a device comprising a semiconductor, which semiconductorcomprises:

-   -   (a) a metal halide perovskite; and    -   (b) a passivating agent which is an organic compound;    -   wherein molecules of the passivating agent are disposed at grain        boundaries within the metal halide perovskite and are not        chemically bonded to anions or cations in the metal halide        perovskite;    -   wherein the process comprises treating a metal halide perovskite        with a passivating agent, which passivating agent is an organic        compound that does not chemically bond to anions or cations in        the metal halide perovskite. As mentioned above for the device        according to the invention, while the invention is typically        applied to metal halide perovskites, the skilled person will        understand that it may be applied to crystalline ionic solids in        general, for instance metal halides and metal oxides.

Thus, in accordance with the first aspect, the invention also provides aprocess for producing a device comprising a semiconductor, whichsemiconductor comprises:

-   -   (a) a crystalline ionic solid; and    -   (b) a passivating agent which is an organic compound;    -   wherein molecules of the passivating agent are chemically bonded        to anions or cations in the crystalline ionic solid,    -   wherein the process comprises treating a crystalline ionic solid        with a passivating agent, which passivating agent is an organic        compound and is suitable for chemically bonding to anions or        cations in the crystalline ionic solid.

Similarly, in accordance with the second aspect, the invention alsoprovides a process for producing a device comprising a semiconductor,which semiconductor comprises:

-   -   (a) a crystalline ionic solid; and    -   (b) a passivating agent which is an organic compound;    -   wherein molecules of the passivating agent are disposed at grain        boundaries within the metal halide perovskite and are not        chemically bonded to anions or cations in the crystalline ionic        solid;    -   wherein the process comprises treating a crystalline ionic solid        with a passivating agent, which passivating agent is an organic        compound that does not chemically bond to anions or cations in        the crystalline ionic solid.

The crystalline ionic solid may be as defined anywhere herein for thedevice according to the invention.

In the process for producing a device according to either the firstaspect of the invention or the second aspect of the invention, any ofthe components may be as described anywhere hereinbefore. Thepassivating agent may be as defined anywhere hereinbefore, and/or themetal halide perovskite may be as defined anywhere hereinbefore, and/orthe device may be as defined anywhere hereinbefore. For instance, themetal halide perovskite may be a perovskite of formula [A][B][X]₃wherein: [A] is at least one organic cation, for instance (CH₃NH₃)⁺; [B]is at least one metal cation, wherein [B] comprises at least one ofCa²⁺, Sr²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Fe²⁺, Co²⁺, Pd²⁺, Ge²⁺, Sn²⁺, Pb²⁺,Sn²⁺, Yb²⁺ and Eu²⁺, preferably Sn²⁺, Pb²⁺, Cu²⁺, Ge²⁺ and Ni²⁺; and [X]is at least one halide anion. Also, for instance, the passivating agentwhich is an organic compound may be selected from (a) a halogen bonddonor compound, for instance IPFB, and (b) an organic compoundcomprising at least one thiol or sulfide group, for instance thiopheneor tetrahydrothiophene. The passivating agents may be chemically bondedby supramolecular chemical bonds, for instance halogen bonds ormetal-chalcogen bonds, such as metal-sulfur bonds. The semiconductor maybe a layer as described anywhere above.

In the first aspect, the passivating agent is typically an organiccompound which is suitable for chemically bonding to anions or cationsin the metal halide perovskite by a supramolecular chemical bond such asa halogen bond or a metal-chalcogen bond. An organic compound issuitable for chemically bonding to anions or cations in the metal halideperovskite if it is energetically favourable for the compound to do so.The skilled person may easily assess whether an organic compound issuitable for chemically bonding to anions or cations in the metal halideperovskite. For instance, it could be observed whether the moleculesadsorb to the perovskite surface. The structure of the organic compoundis also indicative of its suitability for forming chemical bonds, suchas supramolecular chemical bonds, with anions or cations in theperovskite. For instance, to form a halogen bond, the compound maycontain a polarizable or polarized halogen atom. For instance, to form ametal-chalcogen bond, the compound may contain an available (i.e.non-sterically hindered) chalcogen atom, for instance a sulfide group.The passivating agent may be as described anywhere hereinbefore.

For instance, the passivating agent of the first aspect may be suitablefor chemically bonding to anions or cations in the metal halideperovskite by a supramolecular chemical bond such as a nitrogen-metalbond or a phosphorus-metal bond. Passivating agents which are organiccompounds comprising one or more N or P atoms are described above, forinstance pyridine.

In the process for producing a device according to either the firstaspect of the invention or the second aspect of the invention, the metalhalide perovskite may be treated with the passivating agent by anysuitable method. For instance, the passivating agent may be disposed ona surface of the metal halide perovskite, or the metal halide perovskitemay be exposed to a vapour or composition comprising the passivatingagent. For instance, a composition comprising the passivating agent maybe spin-coated onto a surface of the metal halide perovskite. Treatingthe metal halide perovskite with the passivating agent may compriseimpregnating the metal halide perovskite with the passivating agent. Forinstance, the metal halide perovskite may be impregnated with thepassivating agent by immersing the metal halide perovskite in thepassivating agent or a solution comprising the passivating agent. Themetal halide perovskite may be immersed in a composition comprising thepassivating agent.

Sometimes it may be preferable to treat a hot sample with thepassivating agent. For instance, the metal halide perovskite may beheated at a temperature of from 50° C. to 100° C. before it is treatedwith the passivating agent.

Treating the metal halide perovskite with a passivating agent typicallycomprises disposing the passivating agent on a surface of the metalhalide perovskite. Treating the metal halide perovskite with apassivating agent may comprise disposing on a surface of the metalhalide perovskite at least one composition comprising the passivatingagent. In this context, “disposing” includes any method by which thesurface of the perovskite is brought into contact with the materialwhich is disposed, for instance by submerging the metal halideperovskite in a composition. Often, the passivating agent is a liquid atambient temperature (for instance 25° C.). The composition comprisingthe passivating agent may in some embodiments consist only of, orconsist essentially of, the passivating agent, for instance, it maycomprise greater than 95 wt % of the passivating agent. A compositioncomprising the passivating agent may comprise one more solvents and thepassivating agent. The solvent may be selected from an organic solvent,for instance a non-polar solvent such as a hydrocarbon solvent, forinstance pentane, cyclohexane or benzene.

Treating the metal halide perovskite with a passivating agent may alsocomprise adding the passivating agent to a solution of the metal halideperovskite before formation of the metal halide perovskite solid.

In the first aspect the passivating agent may be a halogen-bond donorcompound. If the passivating agent is a halogen-bond donor compound,treating the metal halide perovskite may comprise immersing the metalhalide perovskite in the passivating agent or a composition comprisingthe passivating agent. The metal halide perovskite may be immersed in asolution of the halogen bond donor compound for from 1 to 30 minutes, orfrom 1 to 10 minutes. The concentration of the composition comprisingthe passivating agent may be from 0.05 M to 2.0 M.

The passivating agent of the first aspect may be an organic compoundcomprising at least one thiol or sulfide group. When the passivatingagent is an organic compound comprising at least one thiol or sulfidegroup, the metal halide perovskite is often treated by spin-coating thepassivating agent on a surface of the metal halide perovskite. Spincoating may be carried out at from 1000 to 3000 rpm.

The passivating agent of the first aspect may be an organic compoundcomprising at least one heteroatom selected from N and P. When thepassivating agent is an organic compound comprising one or more N or Patoms, the metal halide perovskite is often treated by spin-coating thepassivating agent or a composition comprising the passivating agent anda solvent on a surface of the metal halide perovskite. Preferably,treating the metal halide perovskite with a passivating agent which isan organic compound comprising one or more N or P atoms comprisesspin-coating a composition (for instance a solution) comprising thepassivating agent and a solvent, wherein the amount of the passivatingagent is from 5 to 50 vol % of the composition. The compositioncomprising the solvent and the passivating agent preferably comprisesfrom 10 to 20 vol % of the passivating agent. The solvent may be anysuitable solvent and is typically an organic solvent, for instancechlorobenzene, toluene or isopropanol.

Once the metal halide has been treated, it may be dried. For instance,the treated metal halide perovskite may be dried by heating, by leavingexcess passivating agent to evaporate or by drying under a nitrogenflow. If the passivating agent is a halogen bond donor compound, thetreated metal halide perovskite may be dried under a flow of nitrogen.

The metal halide perovskite may be treated with the passivating agent inair or in an inert atmosphere, for instance nitrogen.

The process for producing a device typically comprises: (a) providing asubstrate having a layer comprising the metal halide perovskite disposedthereon; and (b) treating the layer comprising the metal halideperovskite with the passivating agent. The layer comprising the metalhalide perovskite may be a layer of the metal halide perovskite.

The substrate having a layer comprising the metal halide disposedthereon may be prepared by providing a substrate and disposing a layerof perovskite thereon. The layer comprising the metal halide perovskitemay be produced by solution deposition or vapour deposition. Producing alayer of metal halide perovskite by vapour deposition typicallycomprises: (i) exposing the substrate to vapour, which vapour comprisessaid metal halide perovskite or one or more reactants for producing saidperovskite; and (ii) allowing deposition of the vapour onto thesubstrate, to produce a solid layer of said perovskite thereon. Theperovskite in the vapour may be any of the metal halide perovskitesdiscussed hereinbefore for the device of the invention, and is typicallya perovskite of formula (I) as defined hereinbefore. If one or morereactants for producing the metal halide perovskite are used, the one ormore reactants may comprise: (a) a first compound comprising (i) a metalcation and (ii) a first halide anion; with (b) a second compoundcomprising (i) an organic cation and (ii) a second halide anion. Thefirst and second halide anions may be different halide anions. Forinstance, the first compound may be a metal halide, such as a leaddihalide, and the second compound may be a halide of the organic cation,for instance a methylammonium halide. For instance, when the metalhalide perovskite being deposited is CH₃NH₃PbI₂Cl, the one or morereactants typically comprise (a) PbI₂, and (b) CH₃NH₃Cl.

The vapour deposition process generally further comprises producing thevapour in the first place by evaporating said perovskite or evaporatingsaid one or more reactants for producing said perovskite. In this stepthe perovskite or the one or more reactants for producing the perovskiteare typically transferred to an evaporation chamber which issubsequently evacuated. The perovskite or the one or more reactants forproducing the perovskite are typically then heated. The resulting vapouris then exposed to and thereby deposited the first region, to produce asolid layer of said perovskite thereon. If reactants are used, thesereact together in situ to produce the perovskite on the first region.Typically, the vapour deposition is allowed to continue until the solidlayer of perovskite has a desired thickness, for instance a thickness offrom 10 nm to 100 μm, or more typically from 10 nm to 10 μm. Preferably,the vapour deposition is allowed to continue until the solid layer ofperovskite has a thickness of from 50 nm to 1000 nm, for instance from100 nm to 700 nm, or any of the thicknesses defined above for the deviceof the invention, for instance greater than or equal to 100 nm.

The step of disposing the layer of metal halide perovskite by vapourdeposition usually further comprises: (iii) heating the solid layer ofthe perovskite thus produced. The step of heating the solid layer of theperovskite usually comprises heating the solid layer of the perovskitein an inert atmosphere. Typically, the temperature at which the solidlayer of the perovskite is heated does not exceed 150° C. Thus, thesolid layer of the perovskite may be heated at a temperature of from 30°C. to 150° C., and is preferably heated at a temperature of from 40° C.to 110° C. The solid layer of the perovskite may be heated at saidtemperature until it has the desired semiconducting properties. Usually,the solid layer of the perovskite is heated for at least 30 minutes,preferably for at least 1 hour.

The layer of the metal halide perovskite may be disposed by solutiondeposition. For instance, the layer of the metal halide may be disposedon the substrate by a process comprising: (i) disposing a precursorsolution on the substrate, which precursor solution comprises said metalhalide perovskite dissolved in a solvent; and (ii) removing the solventto produce on the first region a solid layer of the perovskite. Usually,the steps of (i) disposing a precursor solution on the substrate, and(ii) removing the solvent, comprise spin coating or slot-dye-coating theprecursor solution or solutions onto the substrate, to produce on thesubstrate layer of the perovskite. Typically, said coating is carriedout in an inert atmosphere, for instance under nitrogen. The spincoating is often performed at a speed of from 1000 to 2000 rpm. The spincoating may for example be carried out for 30 seconds to 2 minutes. Theprecursor solution may comprise a solution of the metal halideperovskite, or it may comprise a solution of a first and a secondcompound as described above for the vapour deposition method.

The substrate having a layer comprising the metal halide disposedthereon may comprise several other layers. For instance, the substratehaving a layer comprising the metal halide disposed thereon may compriseone or more layers selected from: a layer of a substrate material, alayer of an electrode material, an n-type layer, a p-type layer and alayer of a scaffold material. The substrate material may comprise aglass, a metal or a plastic, for instance polyethylene. The electrodematerial may be any suitable conductive material, for instance a metalor a transparent conducting oxide. Thus, the layer of an electrodematerial may comprise a metal, for instance, gold, silver, copper, oraluminium, or a transparent conducting oxide, for instance indium tinoxide (ITO) or fluorine-doped tin oxide (FTO).

The substrate having a layer of metal halide perovskite disposed thereonmay comprise a first electrode material and at least one first regionselected from an n-type region, a p-type region or an intrinsic region.Often, the substrate comprises a first electrode material and an n-typeregion. The substrate may comprise a first electrode material which is atransparent conducting oxide, for instance FTO or ITO. The substrate maycomprise a n-type region which comprises an n-type layer as definedanywhere hereinbefore. For instance, the substrate may comprises a layerof a transparent conducting oxide and an n-type layer, for instancetitania. The substrate may comprise a compact layer of TiO₂.

If the substrate comprises a layer of a first electrode material, thelayer of the first electrode material may have a thickness of from 100nm to 200 nm. If the substrate comprises an n-type layer, the n-typelayer may have a thickness of from 50 nm to 500 nm.

Often, the substrate may comprise a porous layer of a scaffold material.The scaffold material may be as described anywhere herein. The substratehaving a layer of a perovskite disposed thereon may comprise a porouslayer of a scaffold material, wherein the porous layer of a scaffoldmaterial comprises an n-type semiconductor or a dielectric material. Thescaffold material may be a dielectric material or an n-type material.For instance, the scaffold material may be selected from alumina (Al₂O₃)or titania (TiO₂). The porous layer of the scaffold material may have athickness of from 5 nm to 500 nm, or from 100 nm to 300 nm.

The process for producing a device may alternatively comprises: (a)disposing a precursor solution on a substrate, which precursor solutioncomprises said metal halide perovskite and the passivating agentdissolved in a solvent; and (ii) removing the solvent to produce a solidlayer of the passivated metal halide perovskite. This alternativeprocess may be as described anywhere herein.

Often, after the metal halide perovskite has been treated with thepassivating agent, the process for producing a device further comprisesdisposing on the layer comprising the metal halide perovskite: (c) atleast one second region selected from an n-type region, a p-type regionor an intrinsic region; and/or (d) a layer of a second electrodematerial. The process for producing a device may further comprisedisposing on the layer comprising the metal halide perovskite: (c) atleast one second region selected from an n-type region, a p-type regionor an intrinsic region; and (d) a layer of a second electrode material.

The step (c) of disposing a second region selected from an n-typeregion, a p-type region or an intrinsic region on the layer of metalhalide perovskite may be carried out by any suitable method. Often thesecond region is selected from an n-type region or a p-type region. Ifthe first region comprises an n-type region, the second region istypically a p-type region. The n-type region may comprise an n-typelayer as defined anywhere hereinbefore. The p-type region may comprise ap-type layer as defined anywhere hereinbefore. The intrinsic region maycomprise any intrinsic semiconductor, for instance crystalline silicon.

The disposal of a p-type region or an n-type region on the layer of themetal halide perovskite may comprise depositing layer by spin coating orby slot-dye-coating the compound comprised in the layer or a precursorthereof, or by spray pyrolysis. For instance, a compact layer of titaniamay be produced by spin-coating a (mildly) acidic titanium-isopropoxidesol in a suitable solvent, such as ethanol. Such a sol can be preparedby mixing titanium isopropoxide and anhydrous ethanol with a solution ofHCl in anhydrous ethanol. After spin-coating, the layer is typicallydried at a temperature not exceeding 150° C. Optionally, the compactlayer was subsequently heated to 500° C. for 30 minutes on a hotplate inair. Alternatively, such a compact layer may be produced by, spraypyrolysis deposition. This will typically comprise deposition of asolution comprising titanium diisopropoxide bis(acetylacetonate),usually at a temperature of from 200 to 300° C., often at a temperatureof about 250° C. Usually the solution comprises titanium diisopropoxidebis(acetylacetonate) and ethanol, typically in a ratio of from 1:5 to1:20, more typically in a ratio of about 1:10. Such methods can beapplied to other p-type or n-type materials, to produce n-type andp-type layers in the devices of the invention.

Deposition of an organic, molecular or polymeric p-type layer may beachieved by spin-coating a solution of the material in a suitablesolvent onto the layer of the passivated metal halide perovskite. Thep-type hole transporter, for instance, spiro-OMeTAD, is typicallydissolved in chlorobenzene. Usually the concentration of spiro-OMeTAD inchlorobenzene is from 150 to 225 mg/ml, more usually the concentrationis about 180 mg/ml. An additive may be added to the hole transporter orelectron transporter material. The additive may be, for instance, tBP,Li-TFSi, or an ionic liquid.

Usually, the second electrode material comprises a high work functionmetal, for instance gold, silver, nickel, palladium or platinum, andtypically silver. Usually, the thickness of the second electrode is from50 nm to 250 nm, more usually from 100 nm to 200 nm. For example, thethickness of the second electrode may be 150 nm. The second electrode istypically disposed on the second region by vapour deposition. Often, thestep of producing a second electrode comprises placing a film comprisingthe hole transporting material in a thermal evaporator. Usually, thestep of producing a second electrode comprises deposition of the secondelectrode through a shadow mask under a high vacuum. Typically, thevacuum is about 10⁻⁶ mBar. The second electrode may, for example, be anelectrode of a thickness from 100 to 200 nm. Typically, the secondelectrode is an electrode of a thickness from 150 nm.

As the layer comprising the metal halide perovskite has been passivatedby the treatment described in step (b), the steps (c) and (d) may becarried out upon a passivated surface of the metal halide perovskite.There may therefore be an intervening layer, for instance a monolayer,of the passivating agent between the layer of the metal halideperovskite and the second region and/or the layer of the secondelectrode material.

For instance, step (c) may comprise spin-coating a solution comprising2,2′,7,7′-tetrakis-(N,N-di-pmethoxyphenylamine)9,9′-spirobifluorene(Spiro-OMeTAD) and an organic solvent, for instance chlorobenzene. Theconcentration of the solution may be from 50 mM to 200 mM. The solutionmay further comprise tert-butylpyridine (tBP) (optionally at aconcentration of from 70 to 90 mol %) and lithiumbis(trifluoromethanesulfonyl)imide (Li-TFSI), optionally about 30 mol %of Li-TFSI.

Additionally or alternatively, step (c) may for instance compriseevaporating a silver electrode onto the device through a shadow mask.The silver electrode may have a thickness of from 100 nm to 100 nm.

The device may be an optoelectronic device, for instance a photovoltaicdevice. Thus, the device may be selected from a photodiode, a solarcell, a photodetector, and a photosensor.

A process for producing a device according to the invention may compriseone or more of the following steps:

-   -   I. providing a substrate comprising a first layer of a first        electrode material, optionally a layer of semi-transparent        fluorine-doped tin oxide (FTO);    -   II. depositing a layer of an n-type material, for instance a        compact layer of TiO₂, on the layer of the first electrode        material;    -   III. heating the substrate comprising the layer of the first        electrode material and/or the layer of the second electrode        material, optionally at from 200° C. to 600° C., optionally for        from 30 min to 60 min;    -   IV. depositing a layer of a mesoporous dielectric material, for        instance Al₂O₃, by spin coating a colloidal dispersion of        nanoparticles of the dielectric material in a solvent, which        solvent may be isopropanol;    -   V. spin-coating a metal halide perovskite precursor, which metal        halide perovskite precursor typically comprises from 10 to 50 wt        % of a first reactant, for instance methylammonium iodide, and a        second reactant, for instance lead (II) chloride, optionally at        3:1 molar ratio in a solvent, for instance dimethylformamide;    -   VI. pre-heating the perovskite precursor and the substrate to        from 60° C. to 80° C. prior to step V;    -   VII. annealing the deposited layer of perovskite at from 80° C.        to 120° C. for from 30 min to 60 min;    -   VIII. treating the, optionally hot (e.g. from 80° C. to 120°        C.), samples with the passivating agent and optionally        thereafter drying under a nitrogen flow;    -   IX. spin-coating a layer of a hole transporting material, for        instance Spiro-OMeTAD; and    -   X. evaporating a layer of a second electrode material, for        instance silver, onto the devices through a shadow mask.

The invention also provides a device obtainable by a process forproducing a device according to the invention.

Passivated Metal Halide Perovskite Semiconductor

The invention also provides a semiconductor which comprises: (a) a metalhalide perovskite; and (b) a passivating agent which is an organiccompound; wherein molecules of the passivating agent are chemicallybonded to anions or cations in the metal halide perovskite.

The passivated metal halide perovskite according to the invention may beas described anywhere hereinbefore for a device, or process forproducing a device according to the invention. For instance, thepassivating agent may be chemically bonded to anions or cations in themixed halide perovskite by supramolecular bonds, for instance halogenbonds or chalcogen-metal bonds. The passivating agent may be selectedfrom (a) a halogen bond donor compound, and (b) an organic compoundcomprising at least one thiol or sulfide group. The passivating agentmay be an organic compound comprising at least one N or P atom such asthose described herein, for instance pyridine.

EXAMPLES Example 1 Adsorption of IPFB and Nature of Interaction

To demonstrate the presence of adsorbed IPBF (iodopentafluorobenzene)and the nature of the interaction with the CH₃NH₃PbX₃ crystal surface(X=halide), solid state ¹³C and ¹⁹F nuclear magnetic resonance (NMR)measurements were performed. FIG. 1e shows the chemical shift of ¹³C NMRfor pure IPFB, which is liquid at room temperature, and for IPFBadsorbed on the perovskite surface. No significant shift was found forthe fluorine-bound carbons (C₂₋₆) in the range 135-150 ppm, while thesignal of the iodine-bearing carbon (C₁) shifted 2 ppm downfield. Thus,¹³C NMR gives strong evidence that IPFB is adsorbed via halogen bondingto the CH₃NH₃PbX₃ crystal surface, as illustrated in FIG. 1 d.

FIG. 1f shows ¹⁹F NMR collected on the same samples, which allows theextraction of more detailed information than ¹³C NMR. The ¹⁹F IPBFsignals recorded on the treated perovskite films are made of twocomponents (inset FIG. 1f ), one small component at the same frequencyas liquid IPBF and one much more intensely shifted by about 0.5 ppmupfield. This supports the conclusion that the IPFB molecules areadsorbed onto the crystal surface and most of the unabsorbed excess isremoved.

Example 2 Passivation Procedure in Meso-Superstructured Solar Cells(MSSCs) with IPFB

The devices were prepared on patterned semi-transparent fluorine-dopedtin oxide (FTO). A compact layer of 70 nm thick TiO₂ was deposited viaspray pyrolysis at 275° C. from a precursor solution of titaniumdiisopropoxide bis(acetylacetonate) diluted with anhydrous ethanol at avolume ratio of 1:10. The substrate was sintered at 500° C. for 45 minand left to cool to room temperature. The samples were then submerged ina 15 mM aqueous TiCl₄ bath at 70° C. for 1 h, followed by rinsing withdeionized water and re-sintering at 500° C. for 45 min. The next layerof mesoporous Al₂O₃ was deposited by spin coating a colloidal dispersionof Al₂O₃ nanoparticles in isopropanol (Sigma-Aldrich) diluted withisopropanol at a volume ratio of 1:2, at 2000 rpm (ramp: 2000 rpm/s) for60 s, followed by drying at 150° C. for 30 min. The perovskite precursor(40 wt % of methylammonium iodide (CH₃NH₃I) and lead (II) chloride(PbCl₂) 3:1 molar ratio in dimethylformamide) was spin coated at 2500rpm (ramp: 2500 rpm/s) for 60 s. The procedure utilized “hot substratespin coating”, i.e., the perovskite precursor and the samples arepre-heated to 70° C. The substrate was transferred quickly to the spincoater; the precursor solution was deposited immediately afterwards andthe spin coating was started. This procedure has yielded consistentlythicker capping layers of perovskites and higher short circuit currents.

The perovskite forms after subsequent annealing at 100° C. for 45 min.Then, the hot samples were directly immersed in aniodopentafluorobenzene (IPFB, Chemical Abstract Services Number827-15-6) solution for a few minutes and thereafter dried under anitrogen flow. Subsequently, the hole transporting material wasdeposited by spin coating (at 2000 rpm, ramp: 2000 rpm/s for 60 s) 80 mM2,2′,7,7′-tetrakis-(N,N-di-pmethoxyphenylamine)9,9′-spirobifluorene(Spiro-OMeTAD) in chlorobenzene with added 80 mol % tert-butylpyridine(tBP) and 30 mol % of lithium bis(trifluoromethanesulfonyl)imide(Li-TFSI). Finally, 150 nm thick silver electrodes were evaporated ontothe devices through a shadow mask.

Example 3 Performance and Optical Properties of MSSCs with IPFB

JV characteristics of the best perovskite MSSCs with and without IPFBtreatment (produced by the above described method) are shown in FIG. 2a. Upon IPFB treatment, the short-circuit current density (Jsc) as wellas the open-circuit voltage (Voc) remain similar, while the fill factor(FF) is dramatically improved. The table inset in FIG. 2b shows that theoverall PCE (power conversion efficiency) increases from 13% to over16%, representing a step improvement. In FIG. 2b the PCE statisticaldistribution for a set of devices prepared simultaneously is shown,which confirms the improved trend.

In FIG. 2a , the control device exhibits a slight bend in the JV curvenear 0.9 V, which is responsible for the relatively poor fill factor.Similarly shaped JV curves have previously been reported in severalworks for both organic and inorganic solar cells, and it is beengenerally referred to as an “S-shaped” JV curve (Kumar, A. et al.,Journal of Applied Physics 105 (2009); Wagenpfahl, A. et al., PhysicalReview B 82, 115306 (2010)). The origin of the S-shape has beenattributed to an energetic barrier for charge extraction, which mayoccur at any interface in the device. Often the interface between thep-type component and the electrode has been found to be responsible. Fewstudies so far have focused on the interface between the n- and p-typecomponent. If the inorganic components are ionic crystals, such as theperovskites used herein, then native dipoles may occur at theorganic-inorganic interface, between the hole transporter and theperovskite. Indeed, the presence of under-coordinated halides at thecrystal surface give rise to local excess of negative electrostaticcharge, which may trap the holes injected into the Spiro-OMeTAD,generating interfacial dipoles. The IPFB treatment could effectivelyscreen the electrostatic charge of the halides exposed to the crystalsurface and prevent dipole formation. Though the S-shape is sometimesunclear, devices with the IPFB passivation treatment systematicallyexhibit improved fill factor.

It was also investigated whether the IPFB adsorption, as represented inFIG. 2c , has changed the optical properties of the perovskite materialitself. In FIG. 2d , the light absorption spectra between 500 nm and2500 nm is shown, which exhibits virtually no differences with andwithout the IPFB. The sub-band gap absorptions (at longer wavelengthsthan 800 nm) are may be significant and not simply due to lightscattering.

Example 4 Photodynamics of IPFB Passivated MSSCs

In order to better understand the evolution of photoinduced species, andto elucidate the dynamics of charge transfer and recombination occurringat the perovskite/hole transporter interface, transient absorption (TA)measurements in the femto-microsecond time window were performed oncomplete perovskite MSSCs, with and without the IPFB treatment. FIG. 3ashows the TA femtosecond spectra in the near infrared, covering the850-1150 nm spectral region. The control sample with no IPFB treatmentshows a flat negative band (photoinduced absorption, PA) at 200 fs,which is quickly overtaken by the formation of a broad positive band(photobleaching, PB) on sub-picosecond time scale. This broad PB band onneat perovskite films (no hole-transporter) was also observed inquasi-steady-state photoinduced absorption. Since this is distinct fromphotoluminescence, and is also present in the neat perovskite films, itmay be assigned to bleaching of absorption into mid-gap states, i.e.charges trapping in mid gap states. With the IPFB treatment, thetransient absorption evolution is considerably different. The PA at 200fs is still observed, however, it evolves into a different PA bandbefore we are able to observe PB on the picosecond time scale. This newPA is clearly evident in the 1 ps trace, extends further in the nearinfrared, and is coincident with the absorption of the positive chargeon Spiro-OMeTAD. The PA band still competes with the formation of thebroad PB band observed without the IPFB, which overbears the PA only onpicosecond time scale. This indicates that the surface treatment makesthe hole transfer process to the Spiro-OMeTAD dominating with respect tothe occupancy of mid-gap stats on the sub-picosecond time scale uponphotoexcitation. This does not necessarily imply that hole-transfer ismore efficient with IPFB, but it does signify that there is less or aslower filling of mid-gap states with the IPFB treatment.

To probe a signature of hole-transfer from the perovskite to theSpiro-OMeTAD, a transient photoluminescence quenching experiment wasperformed. In FIG. 3b it is shown that the Spiro-OMeTAD quenches thephotoluminescence of the perovskite at similar, though fractionallyfaster rates with the IPFB treatment. Disentangling all the absorptionfeatures is challenging, however the results above are consistent with asmaller and slower build-up occupied of mid-gap states and faster holetransfer to the Spiro-OMeTAD when the perovskite film is treated withIPFB.

To probe the charge recombination dynamics at the perovskite/holetransporter interface, the decay of the TA signal for the oxidizedSpiro-OMeTAD species in the nano-millisecond time scale was measured. InFIG. 3c , the TAS dynamics probed at 640 nm from samples with andwithout the IPFB passivation is shown. In the untreated sample, theholes recombine with an initial time constant of approximately 300 ns.By contrast, the IPFB treated sample shows a much longer decay with aninitial time constant of approximately 900 ns. Thus, the hole-lifetimeis more than 3 times longer, indicating that the hole recombination issignificantly suppressed with the presence of IPFB.

Example 5 Perovskite/Hole Transporter Interface Investigation

In order to fully understand what happens at the perovskite/holetransporter interface under different device working conditions, smallperturbation photocurrent and photovoltage decay measurements were used.Since the lifetime for the charge transport in MSSC devices is close tothe instrument resolution of the apparatus, perovskite-sensitized solarcells (PSSCs) (which replace the thin (300 nm) Al₂O₃ which are found inMSSCs with thick (1.5 μm) mesoporous TiO₂) were constructed. The deviceswere constructed by the method of Example 2, except Al₂O₃ was replacedwith TiO₂. The perovskite is then deposited on the mesoporous TiO₂. Inthe PSSC configuration, the charge transport can be moderated, forcingthe electron transport to be exclusively through the TiO₂, by makingthick mesoporous TiO₂ films, with a relatively low coating density ofperovskite. Similar enhancements in solar cell performance with the IPFBtreatment were observed. The relative change in charge recombination atperovskite/hole transporter interface in working devices can be observedby plotting the recombination lifetimes (τ_(rec)) against the relativeposition of the electron quasi-Fermi level with respect to theconduction band edge in the TiO₂ (V_(cbe)−V_(F)). FIG. 4a shows that theIPFB treatment reduces the recombination rate constant (1/τ_(rec)) atthe perovskite/hole transporter interface by a factor of three,consistent with the TA results presented in FIG. 3 d.

Although the inhibition of recombination could explain the improved fillfactor observed with the IPFB treatment, it does not clarify theoccurrence of the S-shaped JV curve. As illustrated in FIG. 4b ,under-coordinated halides (X⁻) at the crystal surface could act as trapsites for the holes on Spiro-OMeTAD. If this is the case, then holesshould accumulate at this heterojunction until they have screened all ofthe under-coordinated halides. Therefore, it would be expected to seeadditional build-up of positive charge in the control device. Therelative concentration of this accumulated charge can be directlyestimated by comparing the total charge extracted under short circuitcondition (ρ_(sc)) at the same J_(sc).

FIG. 4c shows that, for any given J_(sc), there is a much largerbackground density of charge within the devices without the IPFBtreatment. This is consistent with IPFB effectively passivating theunder-coordinated halides and reducing the density of accumulated chargeat the heterojunction, as illustrated in FIG. 4d . Remarkably, theadditional background charge density in the control devices issignificantly larger than the total charge density in the IPFB treateddevice. It is proposed that the S-shaped JV curve arises from holeaccumulation in the Spiro-OMeTAD at the perovskite/hole transporterheterojunction, which results in a local electric field causing holedrift within the Spiro-OMeTAD towards, rather than away from, theheterojunction. The effect of this electric field may be negligible inshort circuit conditions, but it becomes significant under externalapplied bias.

Example 6 Passivation of Tin Halide Perovskites with IPFB

Layers of perovskite containing varying amounts of the tin halideperovskite, CH₃NH₃SnI₃ were deposited on a substrate comprising a glasssubstrate, an FTO layer, a compact TiO₂ layer and a mesoporous TiO₂layer in a nitrogen filled glove box on glass and then treated with IPFBas described above. A layer of spiro-OMeTAD was then spin coated on topof the IPFB passivated tin perovskite. As can be seen in FIG. 5, thelayers passivated with IPFB did not degrade after 25 hours, whereassubstantial degradation can be seen in the un-passivated CH₃NH₃SnI₃films. For a typical organolead mixed halide perovskite, the precursormaterials, CH₃NH₃I and PbCl₂ are dissolved in DMF in a 3:1 molar ratioat a concentration of 40 wt %. The same is done for the mixed metal (tindoped) perovskites, where the total mass of the metal halide remains thesame; but a fraction of the lead halide is replaced by a tin halide. Forexample, for a 25% Sn doped solution, 25% of the total mass of the metalhalide added to the perovskite solution, is comprised of the Sn halide.The 100% methylammonium triiodostannate was fabricated in the same wayas the mixed halide lead perovskite. These Sn based perovskites can alsobe mixed halide perovskites, by using SnCl₂, SnF₂, SnBr₂.

Example 7 Passivation Procedure in MSSCs with Thiophene

FTO-coated glass sheets (15 Ωcm⁻¹ Pilkington) were etched with zincpowder and HCl (2M) to obtain the required electrode pattern. The sheetswere then washed with soap (2% Hellmanex in water), deionized water,acetone, and ethanol, and treated under oxygen plasma for 10 minutes toremove any remaining organic residue. Subsequently, a compact layer ofTiO₂ was deposited by spin-coating a solution of titanium isopropoxidein ethanol onto the substrate. The substrate was then sintered to 500°C. for 45 mins. An aluminium oxide (Al₂O₃) dispersion, diluted 2:1(IPA:Al₂O₃) was then spin coated onto the substrate and subsequentlydried for an hour. A 40 wt % solution of mixed halide perovskite(CH₃NH₃PbI_(3-x)Cl_(x)) was then spin coated onto the Al₂O₃ in theglovebox, and the substrates were left to dry at ambient temperature for30 mins, then annealed at 100° C. for 90 mins.

After annealing of the perovskite, a passivating layer (thiophene) wasspin coated onto the hot substrate. The hole transporting material(HTM),2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)9,9′-spirobifluorene(spiro-OMeTAD), was dissolved in chlorobenzene at 13 vol %, and thenheated to 100° C. until it was completely dissolved. After completedissolution, 4-tert-butyl pyridine (tBP) was added in a volume-to-massratio of 1:26 μL mg−1 tBP:Spiro-OMeTAD. Lithiumbis(trifluoromethylsulfonyl)imide salt (Li-TFSI) was pre-dissolved inacetonitrile at 170 mgmL⁻¹, and added to the hole transporter solutionat 1:12 μL mg⁻¹, Li-TFSI solution: Spiro-OMeTAD. The HTM was thenspin-coated on the substrate at 1000 rpm for 45 seconds. The films werethen placed in a thermal evaporator, where 200 nm thick silverelectrodes were deposited through a shadow mask under high vacuum (10⁻⁶mbar). The active area of the devices was defined by a metal opticalmask with 0.0635 cm² aperture.

Example 8 Device Characteristics

Device characteristics of MSSCs passivated with tetrahydrothiophene andthiophene produced by the above described method were measured. Thecharacteristics are shown in FIGS. 6 and 7, where they are also comparedwith device characteristics of IPFB passivated devices and un-passivatedcontrol devices. FIG. 6 shows the spread of performances obtained forthree different surface treatments as compared to a control devicewithout any surface treatments. All devices were completely processedwithin the glovebox, and with a sample size of 16 individual devices foreach variable investigated: iodopentafluorobenzene (IPFB),tetrahydrothiophene (THTh), thiophene (Th) and control devices. We seehere that for the passivated devices there is an improvement in deviceparameters when compared to the control. FIG. 7 shows the J-Vcharacteristics of the best performing devices for surface treatmentinvestigated: iodopentafluorobenzene (IPFB), tetrahydrothiophene (THTh),thiophene (Th) and a control device with no surface treatments; as wellas a table showing the maximum values of all the device parameters.

Example 9 Time Resolved Photoluminescence of the Mixed Halide PbPerovskite (CH₃NH₃PbI_(3-x)Cl_(x)) with Various Surface Treatments

Spectroscopy samples were prepared in a nitrogen filled glove box byspin coating films of perovskite precursor on to glass slides. The spincoating protocol uses a 40 wt % solution of 3:1 molar ratio ofCH₃NH₃I:PbCl₂ in DMF. The slides were left to dry for 1 hour in anitrogen filled glove box, after which they were heated to 90° C. for120 mins. After heating the liquid thiophene or IPFB (surfacetreatments) were dispensed onto the substrates and spin coated, followedby a coating with a ˜100 nm layer of poly methylmethacrylate (PMMA)dispensed and spin coated from a toluene based solution. All processingwas done in a nitrogen filled glove box. The results are given in FIG. 8which shows that while IPFB has a small effect on the PL(photoluminescence) lifetime of the films, there is an increase inlifetime with the thiophene. When a combination of thiophene and IPFBwere spin coated onto the films (Thiophene followed by IPFB) the PLlifetime of the films increased considerably, demonstrating a reductionin the non-radiative decay rate (or channels) after the surfacetreatments. This data is interpreted as implying that the combination ofthese materials passivates under-coordinated bonds in the material. Thedata therefore implies that the undercoordinated ions are responsiblefor creating non-radiative electron and hole recombination sites.

Example 10 Steady State Photoluminescence of the Mixed Halide Perovskite(CH₃NH₃PbI_(3-x)Cl_(x)) with Various Surface Treatments

FIG. 9 shows the steady state photoluminescence (PL) of a film ofCH₃NH₃PbI_(3-x)Cl_(x) coated on glass substrates (same samples as usedfor the measurement in FIG. 8). As seen in the time resolved PL, theIPFB treatment has little effect on the PL of the material. However, anincrease in the photoluminescence is seen with the thiophene treatment,and a further increase by using a combination (combo) of thiophene andIPFB, further evidence that these two treatments act to passivate trapstates in the material.

Example 11 Passivation and Stabilisation of Methylammonium Tin Triiodide

A passivating layer of thiophene was spin coated onto a thick layer ofmethylammonium tin triiodide (CH₃NH₃SnI₃, formed under an inertatmosphere). The sample was then left in air at ambient indoorconditions for three weeks. The absorption spectrum of this three weekold sample is shown in FIG. 10. While CH₃NH₃SnI₃ has in the past beenconsidered notoriously unstable, FIG. 10 demonstrates that theabsorbance of the sample passivated with thiophene has remained stablefor three weeks.

Example 12 Device Performance with and without IPFB Treatment

Devices were prepared by the process described in Example 2 withdifferent mesoporous Al₂O₃ thicknesses (100 nm, 400 nm, 600 nm, and 1500nm). All devices were prepared simultaneously with and without the IPFBtreatment. The device performance characteristics were then measured,and a box chart of device parameters extracted from the current-voltagecharacteristics are shown in FIG. 11 (where each point represents asingle device). The IPFB treatment results in a substantial improvementof power conversion efficiency and fill factor when compared withuntreated devices.

Example 13 Device Performance with Treatment Using DifferentIodoperfluorcarbons

MSSCs were constructed by the method of Example 2, except that differentiodoperfluorocarbons were used in addition to IPFB. The differentiodoperfluorocarbons used were: iodopentafluorobenzene (IPFB),perfluoro-n-butyl iodide (PFBI), perfluoro-n-hexyl iodide (PFHI) andperfluorodecyl-n-iodide (PFDI). FIG. 12 shows a box chart of deviceparameters extracted from the current-voltage characteristics of thedevices.

Example 14 Device Performance Parameters for Perovskite Sensitized SolarCells (PSSCs) with 1.5 μm Thick Mesoporous TiO₂, with and without IPFBTreatment

PSSCs with 1.5 μm thick mesoporous TiO₂ were prepared by the method ofExample 5 with and without IPFB treatment. The device performancecharacteristics were then measured, and a box chart of device parametersextracted from the current-voltage characteristics are shown in FIG. 13(where each point represents a single device). All devices were preparedsimultaneously with and without the IPFB treatment as described inMethods.

Example 15 Photovoltage and Photocurrent Decay Measurement for DSSCs,with and without IPFB

Dye sensitized solar cells (DSSCs) were prepared by disposing an organicdye on a mesoporous TiO₂ layer prepared by the method of Example 5(where perovskite was replaced with dye D102), with and without IPFBtreatment. Photovoltage-current decay measurements for devices preparedwith organic dye (D102), were extracted from four separate devices. Theresults are shown in FIG. 14: a) Charge density at short circuit(ρ_(sc)) against short circuit photocurrent (J_(sc)); b) charge densityat open circuit (ρ_(oc)) against the open circuit voltage (V_(oc)); c)recombination lifetimes at open circuit conditions (τ_(rec)) againstcharge density at open circuit (ρ_(oc)); d) transport lifetimes at shortcircuit conditions (τ_(trans)) against charge density at short circuit(ρ_(sc)).

Example 16 Photoluminescence Data for Pyridine Passivated Films

Spectroscopy samples were prepared by spin coating films of perovskiteon to glass slides. The spin coating protocol uses a 40 wt % solution of3:1 molar ratio of CH₃NH₃I:PbCl₂ in DMF. The slides were left to dry for1 hour, after which they were heated to 90° C. for 120 mins. Afterheating the surface treatments (pyridine or tertbutylpyridine (tBP)diluted to 10 to 20 vol % in chlorobenzene) were spin coated onto thesubstrates, followed by a 100 nm layer of PMMA (using a 1% solution ofpoly methyl methacrylate). All processing was done in inert atmosphere.The steady state photoluminescence (PL) and photoluminescence quantumefficiency (PLQE) of the passivated and unpassivated (control) films areshown in FIG. 15. The time resolved PL of passivated and unpassivated(control) films is shown in FIG. 16. These results show that while tBPquenches the PL of the perovskite, there is an increase in lifetime withthe pyridine. With the use of the pyridine the PL lifetime of the filmsincreased considerably up to over a microsecond, suggesting that, likethe thiophene, pyridine passivates under-coordinated bonds in thematerial. The increase in the steady-state PL and the PLQE alsocorroborate this hypothesis.

Example 17 Fabrication of Planar Heterojunction Solar Cells withThiophene or Pyridine

FTO-coated glass sheets (15 Ωcm⁻¹ Pilkington) were etched with zincpowder and HCl (3M) to obtain the required electrode pattern. The sheetswere then washed with soap (2% Hellmanex in water), deionized water,acetone, and methanol, and finally treated under oxygen plasma for 10min to remove the last traces of organic residues. A 100 nm thickcompact layer of TiO₂ was then deposited on the glass using titaniumisopropoxide diluted in anyhydrous ethanol and sintered for 45 mins at500° C. The 40 wt % perovskite precursor solution (3:1 molar ratio ofCH₃NH₃I:PbCl₂ in DMF) was then spin coated directly onto the substrateunder inert atmosphere. The substrate was then left to dry under N₂ for30 min before being placed on a hotplate at 90° C. where it was annealedfor 180 min. After annealing, the substrate was allowed to cool to roomtemperature and a layer of thiophene or pyridine (each 20 vol % inchlorobenzene) was spin coated on top of the perovskite layer, followedby the HTM material as above (Example 7). 150 nm thick silver electrodeswere then deposited through a shadow mask.

The current-voltage characteristics of the devices were measured withhysterisis. The results for a device passivated with pyridine is shownin FIG. 17 (FB is forward bias and SC is short circuit). When startingthe current-voltage scan at FB and scanning towards SC, the shape of thecurrent-voltage curve is different to that scanning from SC to FB. Thisdifference is termed hysteresis in the current-voltage curve. Hysteresisis a non-desirable property of a solar cell and improvements in thesolar cell materials to minimise or reduce hysteresis are highlydesirable. The device in FIG. 17 is a champion pyridine-passivatedplanar-heterojunction device with a PCE of 16.5% which represents a veryhigh efficiency for a single solution deposited perovskite solar cell.The performance characteristics of a batch of passivated andunpassivated solar cells under simulated full sunlight are shown in FIG.18. This demonstrates that the passivated devices consistentlyoutperform the unpassivated devices in every parameter. Notably, thepassivated devices have consistently higher currents and voltages thanare observed in the untreated devices. The device statistics in FIG. 18clearly show that utilising pyridine and thiophene as surfacepassivating agents dramatically improves the reproducibility of devices,markedly reducing the standard deviation. The average performance ofboth thiophene and pyridine treated devices consistently outperform theuntreated control devices. Of the treated devices, pyridine passivateddevices consistently achieve even higher photocurrents and fill factorsthan those treated with thiophene.

FIG. 19 shows device results and stabilised maximum power. FIG. 19(a)shows the current-voltage characteristics of a control device, ascompared to thiophene and pyridine passivated devices. It can be seenthat the pyridine passivated device outperforms both the control and thethiophene passivated device (performance parameters are summarised inTable 1 below). FIG. 19 (b,c,d) show stabilised maximum power output ofpassivated and control devices. It can be seen here that the passivateddevices stabilise at much higher efficiencies and currents than thecontrol device, almost achieving the efficiency of the FB-SC scan.

TABLE 1 Performance parameters extracted from the FB-SC scan of bestcontrol and passivated devices measured under AM1.5 simulatred sun lightof 100 mWcm⁻² equivalent irradiance. Device performance parameters forthe champion devices of each variable, along with the stabilisedefficiency and stabilised current density values. J_(SC) V_(OC) η FFStab. η Stab. J (mA/cm²) (V) (%) (a.u.) (%) (mA/cm²) Pyridine 24.1 1.0516.5 0.72 15.5 21.3 Thiophene 21.3 1.02 15.3 0.68 14.1 20.8 Control 20.70.95 13.1 0.68 8.3 11.8

Utilising the surface treatments on planar heterojunction solar cells,an increase in the maximum power conversion efficiency from 13.1% to15.3% with thiophene passivation and to 16.5% with pyridine passivationhas been observed. These results represent the highest efficiencies wehave achieved for planar heterojunction perovskite solar cellsfabricated using a single step solution deposition method.

In conclusion, a controlled method of surface passivation via coordinatebonding has been demonstrated, which appears to have the effect ofreducing the density of electronic trap sites, which is postulated to becaused by under-coordinated metal ions in the perovskite crystal. Byusing thiophene and pyridine passivation a quantitative and systematicdecrease of defect states is obtained, as opposed to the randomirreproducible nature of atmospheric passivation. A mechanism for thistype of electrical passivation has been proposed and a decrease in therate of non-radiative recombination in perovskite films has been shown.In so doing, the efficiency of planar heterojunction solar cells hasbeen increased from 13% to 15.3% and 16.5% using thiophene and pyridinetreatments respectively, and even more significantly achieved highstabilised power output for these solar cells. Beyond use in solarcells, this passivation technique is likely to prove useful for manyother perovskite based optoelectronic applications such as lasers andLEDs

Solar Cell Characterization

Solar cell performance was measured using a class AAB ABET solarsimulator which was calibrated to give simulated AM 1.5 sunlight at anirradiance of 100 mW/cm². The irradiance was calibrated using anNREL-calibrated KG5 filtered silicon reference cell. Current-Voltagecurves were recorded using a sourcemeter (Keithley 2400, USA). All solarcells were masked with a metal aperture which was used to define theactive area of the devices, which in this case was 0.0625 cm². Alldevices were stored in a desiccator in the dark for 12 hours prior totesting.

Example 18 Photoluminescence Characteristics of Pyridine and ThiophenePassivated Films

To study thiophene and pyridine's impact upon the optoelectronicproperties in more detail the photoluminescence of perovskite filmstreated and untreated with thiophene or pyridine, was investigated.

Spectroscopy samples were prepared by spin coating films of perovskiteon to glass slides. The spin coating protocol uses a 40 wt % solution of3:1 molar ratio of CH₃NH₃I:PbCl₂ in DMF. The slides were left to dry for1 hour, after which they were heated to 90° C. for 120 mins. Afterheating the surface treatments (pyridine or thiophene diluted to 20 vol% in chlorobenzene) were spin coated onto the substrates, followed by a100 nm layer of PMMA (using a 1% solution of poly methyl methacrylate).All processing was done in inert atmosphere.

FIG. 20(b) shows the photoluminescence quantum efficiency (PLQE) whichincreases with excitation power. The PLQE rise with fluence isattributed to a filling of trap states, where the PLQE only reaches apeak value when the trap states, responsible for non-radiativeShockley-Reed-Hall recombination, are predominantly filled. Anorder-of-magnitude increase in the PL lifetime (FIG. 20(a)) of theperovskite films from 300 ns to 1800 ns is also observed when thesurface is treated with pyridine, and to 2200 ns when treated withthiophene. For a given excitation power, an increased PLQE for thepassivated films with respect to the control is seen. The increased PLQEand PL lifetimes both indicate an overall reduction in the rate ofnon-radiative recombination within the material, and are evidence thatsome of the pathways to non-radiative recombination i.e., trap mediatedrecombination, have been substantially reduced. The PLQE for perovskitesamples treated with pyridine is also significantly higher at lowexcitation densities than for the samples treated with thiophene. Ifthis rise in PLQE with excitation power is attributed to the filling oftraps, this is then indicative of the fact that while both pyridine andthiophene act to passivate trap states on the surface of the perovskitematerial, pyridine seems to be more effective, reaching a “plateau” inPLQE at much lower excitation powers. One speculation as to the reasonfor this is that the pyridine may bind more strongly to the perovskitesurface than the thiophene, thus more successfully reducing the degreeof non-radiative recombination.

A model to describe the evolution of photoexcited species (free chargesand excitons) and the subsequent photoluminescence kinetics in thesematerials in the presence of N_(T) sub-gap trap states is proposed.Under photoexcitation, n_(T) traps are filled with electrons, which willresult in a population of n_(T) photodoped holes in the valence band toensure charge neutrality. The untrapped electrons (and their hole pairs)can exist as free charges or as bound excitons (binding energy of 50meV) with a thermal equilibrium established and rapid interchangebetween the species. The intensity-dependent PL decays for bothuntreated and treated samples are shown in FIG. 21. At low fluences,e.g., initial photo-excitation densities of ˜10¹⁵ cm⁻³, recombination isdominated by near-monomolecular recombination between the dominantnumber of photo-doped holes and the minority photo-excited electrons. Athigh fluences (10¹⁷ cm⁻³), traps are predominantly filled and the numberof photo-excited electrons and photo-doped holes are comparable, leadingto a bimolecular decay until low enough density is reached (at longertime) that the decay once more becomes monomolecular.

The results have been globally fitted with the model such that the totalnumber of photogenerated holes, n_(h) at any point in time will be suchthat n_(h)=_(e)+n_(T), where n_(e) is the number of free electrons. Thetotal concentration of photogenerated carriers can then be definedN=n_(e)+n_(x) where n_(x) is the concentration excitons. This howeverexcludes trapped electrons and the corresponding holes. The keyassumption is that the trapped electron is comparatively long lived. Ifwe assume the trap concentration is constant over a PL decaymeasurement, and that during the decay the excitons and free charges arein thermal equilibrium, the model can be fitted to the experimental datato determine the trap density N_(T). From the fitting the trap densityof the untreated film is determined to be 3.5×10¹⁶ cm⁻³. For thethiophene passivated film however, this trap density is decreasedthreefold yielding a trap density of 1.0×10¹⁶ cm⁻³, while for thepyridine passivated film, the extracted trap density is decreased by anorder of magnitude, resulting in a trap density of 0.2×10¹⁶ cm⁻³. Thisis hence consistent with both the thiophene and pyridine treatmentseffectively passivating electronic trap sites in the organic-inorganiclead halide perovskites.

Example 19 Passivation of Lead Halide Perovskites with Varying AlkylChain Length Passivating Agent

The fabrication of CH₃NH₃PbX₃ perovskite film with longer PL lifetime(approx. 1000 ns) as well as with increased inherent hydrophobiccharacter was investigated. This involved studying the variation in thealkyl chain length as a means to introduce a new set of electronic andcrystal properties. In this regard, substituting the methyl group of theCH₃NH₃PbX₃ (where X=I, Br or Cl) perovskite with long alkyl chain length(e.g. octyl-amine group) can induce the reduction of crystallite size ofthe perovskite but when excess of such a long chain is introduced in thecrystal lattice it may completely transform 3D perovskite to 2Dperovskite structure leading to complete change in the structural andelectronic properties of the material.

This study demonstrates that a specific amount of methylaminesubstitution with octylamine group in the CH₃NH₃PbX₃ perovskite shiftsthe steady state PL peak position towards shorter wavelengths, whilstexcessive addition can significantly push the PL from the red towardsthe green region of the emission zone indicating a transformation from a3D to 2D perovskite. This study also demonstrates that the addition of avery small amount of octylamine results in an extraordinary slowing downof the PL decay time. Furthermore, the introduction of the octlyamine tothe CH₃NH₃PbX₃ perovskite makes it more hydrophobic in nature and suchmoisture resistance would then directly influence the long term outdoorstability of the perovskite based device.

Synthesis of alkyl-ammonium-halide

To synthesise methyl-ammonium iodide, 24 ml of Methylamine of 33 wt % inabsolute ethanol was reacted with 10 ml of hydriiodic acid (57% in H₂O)in 100 ml of C₂H₅OH. The reaction was carried out while rigorouslystirring under ambient condition for 30-60 min. The reaction mixture wasthan subjected to a rotary evaporator at 60° C. to remove the solvent,leading to the precipitation of a white/yellowish colouredmethyl-ammonium-iodide powder. The resulting product was then washedwith dimethyl ether to remove un-reacted reactants. Re-crystallizationwas then carried out in either C₂H₅OH or C₂H₅OH/CH₃OCH₃ mixture forfurther purification of CH₃NH₃I (MAI) powder. The resultingrecrystallized MAI was then dried under vacuum furnace at 60° C. untilit become dry. Owing to its hygroscopic nature the purified MAI wasstored in dry condition.

Similar procedures were adapted to synthesize octyl-ammonium-iodide(OAI), octyl-ammonium bromide (OABr) and octyl-ammonium-chloride (OACl).The chain length of the alkyl chain was varied by using the appropriatealkylamine (e.g. octyl-amine). The halide ions were varied by usingdifferent halogen sources (e.g. HBr and HCl etc.). The rest of theprocedures were the same as those used for the methyl-ammonium-iodidesynthesis.

Perovskite Precursor Solution

The perovskite can be synthesized by reacting two compounds, i.e. thealkyl-ammonium halide and lead halide, by the following generalreaction:

CH₃NH₃X+PbX₂->CH₃NH₃PbX₃

Other lead sources that can provide Pb²⁺, such as Pb(CH₃COO)₂, Pb(NO₃)₂can also be used.

In this example the perovskite was synthesised using a 3 molar excess oforganic halide salt to metal halide salt was used with the resultingreaction following:

3CH₃NH₃X+PbX₂->CH₃NH₃PbX₃+by-products

Perovskite Film Fabrication

The precursor solutions was spin coated on to a substrate and thermallyannealed at approx. 100° C. for approx. 45 min. The concentration of theprecursor solution and the annealing protocol can be manipulated as perrequirements. For example, a small increase in the annealing time isrequired when using a 3 molar excess of organic halide salt to metalhalide salt in order to drive off the by-products.

Octylamine Doped (OA) Perovskite Film

In this example, 0, 5, 10, 20 and 70 μl of octylamine (OA) was addedinto 1000, 995, 990, 980 and 930 μl respectively of CH₃NH₃PbI₃ precursorsolution. CH₃NH₃PbI₃ perovskite films were fabricated on glass slidesand then annealed at 100° C. for 45 min. PMMA solution in (10 mg/ml inToluene) was then spin coated to protect from moisture while conductingmeasurements.

FIG. 22(a) shows the steady state PL decay for these OA doped perovskitefilm. A gradual shift towards lower wavelength (blue shift) in PL peakposition with the increasing OA doping concentration can be seen.However, excess addition (e.g. 70ul/l ml perovskite precursor) leads tothe formation of a complete different phase, with a predominant peakappearing at 620 nm. The additional peak at about 620 nm is consistentwith the formation of 2D perovskite phase.

FIG. 22(b) then shows the time resolved PL decay for these OA dopedperovskite. The PL life time increases (as compared to the undopedperovskite film) when a small concentration of OA is added into theprecursor (i.e. 51). Further addition of OA leads to a drastic reductionin the PL life time which may be due to the emergence of secondary phasein the form of 2D perovskite.

Octyl-Ammonium Iodide Doped (OAI) Perovskite Film

In this example, the precursor solution was prepared by using presynthesised OAI, as discussed above, by the following reaction:

3(0.95 mol % CH₃NH₃X+0.05 mol %C₈H₁₇NH₃X)+PbX₂->(0.95CH₃NH₃)(0.09C₈H₁₇NH₃)PbX₃+by-products

The precursor solution was spin coated on to a glass substrate andannealed at 100° C. for 45 min.

FIG. 23 shows the time resolved PL decay measurement on the OAI dopedperovskite film. The controlled substitution of longer alkyl chain forthe methyl group improves the PL lifetime dramatically from just over100 ns to 900 ns as compared to the undoped film, presented in the FIG.22(b).

Mixed Chain Length Perovskite Film Fabrication

By doping the perovskite precursor solution we expect the longer alkylchain amine to be expelled to the surfaces and grain boundaries withinthe bulk of the perovskite film. However, this may also introduce thelonger alkyl group throughout the crystal, which may induce someundesirable electronic properties.

In order to selectively substitute the methyl group from the outerperiphery of the perovskite film, the perovskite thin film can beprepared using the standard perovskite precursor solution describedabove, with the resulting film being immersed into 0.1 M solution of OAI(octyl ammonium iodide) in isopropyl alcohol (IPA). The dipping time andOAI concentration can then be varied depending upon the desired amountof methyl group substitution.

Using this method, it can be expected that the methyl group from outersurface of the perovskite will be substituted and there should benegligible structural change in the perovskite bulk. In this method ahighly hydrophobic perovskite is fabricated.

1. A photovoltaic device comprising a semiconductor, which semiconductorcomprises: (a) a metal halide perovskite; and (b) a passivating agentwhich is an organic compound; wherein molecules of the passivating agentare chemically bonded to anions or cations in the metal halideperovskite.
 2. A photovoltaic device according to claim 1, wherein thechemical bonds between molecules of the passivating agent and anions orcations in the metal halide perovskite are selected from halogen bondsand chalcogen-metal bonds.
 3. A photovoltaic device according to claim 1or claim 2, wherein cations or anions in the metal halide perovskite towhich molecules of the passivating agent are bonded areunder-coordinated.
 4. A photovoltaic device according to any one ofclaims 1 to 3, wherein at least some of the anions or cations in themetal halide perovskite to which molecules of the passivating agent arebonded are at the surface of the metal halide perovskite.
 5. Aphotovoltaic device according to any one of the preceding claims,wherein molecules of the passivating agent form a self-assembled layeron a surface of the metal halide perovskite.
 6. A photovoltaic deviceaccording to any one of the preceding claims, wherein at least some ofthe anions or cations in the metal halide perovskite to which moleculesof the passivating agent are bonded are at defect sites in bulk of thecrystal structure of the metal halide perovskite.
 7. A photovoltaicdevice according to any one of the preceding claims, wherein moleculesof the passivating agent are bonded to under-coordinated cations orunder-coordinated anions in the bulk of the crystal structure of themetal halide perovskite.
 8. A photovoltaic device according to claim 6,wherein at least some of the anions or cations in the metal halideperovskite to which molecules of the passivating agent are bonded are atgrain boundaries in bulk of the crystal structure of the metal halideperovskite.
 9. A photovoltaic device according to any one of thepreceding claims wherein the passivating agent is a compound selectedfrom: (a) a halogen bond donor compound, and (b) an organic compoundcomprising at least one thiol or sulfide group.
 10. A photovoltaicdevice according to any one of the preceding claims, wherein thepassivating agent is a halogen bond donor compound of formula X-EWG,wherein X is a halogen selected from I, Br, Cl and F; and EWG is anelectron withdrawing group.
 11. A photovoltaic device according to anyone of the preceding claims, wherein the passivating agent is a halogenbond donor compound of formula X-EWG, wherein X is a halogen selectedfrom I, Br, Cl and F; and EWG is a group selected from —(CY₂)_(n)Y,—(CY₂)_(n)R, —(CR₂)_(n)Y, —(CR₂)_(n)R, —(CY₂)_(n)CR₃, —(CR₂)_(n)CY₃,—(CY₂)_(n)(CR₂)_(m)Y, —(CR₂)_(n)(CY₂)_(m)Y, —(CY₂)_(n)(CR₂)_(m)R,—(CR₂)_(n)(CY₂)_(m)R, —(CY₂)_(n)(CR₂)_(m)CY₃, —(CR₂)_(n)(CY₂)_(m)CR₃,—(CR_(a)Y_(b))_(n)Y, —(CR_(a)Y_(b))_(n)R, —C₆Y₅, —(C₆R)Y₄, —(C₆R₂)Y₃,—(C₆R₃)Y₂, —(C₆R₄)Y, —CY═CYR, —CY═CR₂, —CR═CYR, —C≡CY, —C≡CR, —COR,—COCYR₂ and —COCY₂R; wherein each Y is the same or different and is ahalogen selected from I, Br, Cl, and F; each R is the same or differentand is a group selected from H, hydroxy, nitrile, nitro, unsubstitutedor substituted C₁₋₁₈-alkyl, unsubstituted or substitutedC₃₋₁₀-cycloalkyl, unsubstituted or substituted C₂₋₁₈-alkenyl,unsubstituted or substituted C₂₋₁₈-alkynyl, and unsubstituted orsubstituted aryl; n is an integer from 1 to 18; m is an integer from 1to 18; each a is the same or different and is 0, 1 or 2; each b is thesame or different and is 0, 1 or 2; and the sum of a and b in eachCR_(a)Y_(b) group is
 2. 12. A photovoltaic device according to any oneof the preceding claims, wherein the passivating agent is a halogen bonddonor selected from X(CY₂)_(m)CY₃ and

wherein X is a halogen selected from I, Br, Cl and F; each Y is the sameor different and is a halogen selected from I, Br, Cl and F; m is 0 oran integer from 1 to 11; and n is an integer from 1 to
 5. 13. Aphotovoltaic device according to any one of the preceding claims,wherein the passivating agent is a halogen bond donor compound selectedfrom I(CY₂)_(m)CY₃ and

wherein each Y is the same or different and is a halogen selected fromI, Br, Cl and F; m is 0 or an integer from 1 to 11; and n is an integerfrom 1 to
 5. 14. A photovoltaic device according to any one of thepreceding claims, wherein the passivating agent isiodopentafluorobenzene.
 15. A photovoltaic device according to any ofthe preceding claims, wherein the passivating agent is an organiccompound comprising at least one thiol or sulfide group, selected from:(i) R¹SH, R¹SR¹, HSR²SH, R¹SR²SR¹, R¹SR²SH,

wherein each R¹ is the same or different and is a group selected fromunsubstituted or substituted C₁₋₁₈-alkyl, unsubstituted or substitutedC₃₋₁₀-cycloalkyl, unsubstituted or substituted C₂₋₁₈-alkenyl,unsubstituted or substituted C₂₋₁₈-alkynyl, and unsubstituted orsubstituted aryl, R² is a group selected from unsubstituted orsubstituted C₁₋₁₈-alkylene, unsubstituted or substitutedC₃₋₁₀-cycloalkylene, unsubstituted or substituted C₂₋₁₈-alkenylene,unsubstituted or substituted C₂₋₁₈-alkynylene, and unsubstituted orsubstituted arylene, and each R³ is the same or different and is a groupselected from H, hydroxy, nitrile, nitro, thiol, halo, amino,unsubstituted or substituted C₁₋₁₈-alkyl, unsubstituted or substitutedC₃₋₁₀-cycloalkyl, unsubstituted or substituted C₂₋₁₈-alkenyl,unsubstituted or substituted C₂₋₁₈-alkynyl, and unsubstituted orsubstituted aryl; and (ii) an oligomer, which oligomer comprises atleast one thiol or sulfide group.
 16. A photovoltaic device according toany one of the preceding claims, wherein the passivating agent isthiophene, 3-hexylthiophene or tetrahydrothiophene.
 17. A photovoltaicdevice according to any one of the preceding claims, wherein thepassivating agent is a halogen bond donor compound, and molecules of thehalogen bond donor compound are bonded to halide anions in the metalhalide perovskite by halogen bonding.
 18. A photovoltaic deviceaccording to any one of the preceding claims, wherein the passivatingagent is an organic compound comprising at least one thiol or sulfidegroup, and molecules of the organic compound are bonded to metal cationsin the metal halide perovskite by sulfur-metal bonds.
 19. A photovoltaicdevice according to any one of claims 1, and 3 to 8, wherein thechemical bonds between molecules of the passivating agent and anions orcations in the metal halide perovskite are selected from nitrogen-metalbonds and phosphorus-metal bonds.
 20. A photovoltaic device according toany one of claims 1, 3 to 8 and 19, wherein the passivating agent is anorganic compound comprising at least one heteroatom selected from N andP.
 21. A photovoltaic device according to any one of claims 1, 3 to 8,19 and 20, wherein the passivating agent is an organic compound selectedfrom a substituted or unsubstituted amine, a substituted orunsubstituted imine, substituted or unsubstituted pyridine, substitutedor unsubstituted pyrrolidine, substituted or unsubstituted pyrrole and asubstituted or unsubstituted phosphine.
 22. A photovoltaic deviceaccording to any one of claims 1, 3 to 8 and 19 to 21, wherein thepassivating agent is an organic compound of formula

wherein R⁴, R⁵ and R⁶ are each independently a group selected from H,unsubstituted or substituted C₁₋₁₈-alkyl, unsubstituted or substitutedC₃₋₁₀-cycloalkyl, unsubstituted or substituted C₂₋₁₈-alkenyl,unsubstituted or substituted C₂₋₁₈-alkynyl, and unsubstituted orsubstituted aryl, and not all R⁴, R⁵ and R⁶ are H, optionally whereintwo or more of R⁴, R⁵ and R⁶ are bonded together to form a ring; each R⁷is independently a group selected from H, unsubstituted or substitutedC₁₋₁₈-alkyl, unsubstituted or substituted C₃₋₁₀-cycloalkyl,unsubstituted or substituted C₂₋₁₈-alkenyl, unsubstituted or substitutedC₂₋₁₈-alkynyl, and unsubstituted or substituted aryl, optionally whereintwo or more R⁷ groups are bonded together to form a ring; R⁸ is a groupselected from H, unsubstituted or substituted C₁₋₁₈-alkyl, unsubstitutedor substituted C₃₋₁₀-cycloalkyl, unsubstituted or substitutedC₂₋₁₈-alkenyl, unsubstituted or substituted C₂₋₁₈-alkynyl; R⁹, R¹⁰ andR¹¹ are each independently a group selected from H, unsubstituted orsubstituted C₁₋₁₈-alkyl, unsubstituted or substituted C₃₋₁₀-cycloalkyl,unsubstituted or substituted C₂₋₁₈-alkenyl, unsubstituted or substitutedC₂₋₁₈-alkynyl, and unsubstituted or substituted aryl, optionally whereintwo or more of R⁹, R¹⁰ and R¹¹ are bonded together to form a ring; and adashed line together with a solid line represents a single or a doublebond.
 23. A photovoltaic device according to claim 22, wherein R⁴, R⁵and R⁶ are each independently a group selected from H and unsubstitutedor substituted C₁₋₃-alkyl, optionally wherein two or more of R⁴, R⁵ andR⁶ are bonded together to form a ring, and optionally wherein at leastone of R⁴, R⁵ and R⁶ is H; each R⁷ is independently a group selectedfrom H and unsubstituted or substituted C₁₋₃-alkyl, optionally whereintwo or more R⁷ groups are bonded together to form a ring; R⁸ is a groupselected from H and unsubstituted or substituted C₁₋₃-alkyl; or R⁹, R¹⁰and R¹¹ are each independently a group selected from H and unsubstitutedor substituted C₁₋₃-alkyl, optionally wherein two or more of R⁹, R¹⁰ andR¹¹ are bonded together to form a ring.
 24. A photovoltaic deviceaccording to any one of claims 1, 3 to 8 and 19 to 23, wherein thepassivating agent is a compound of formula

wherein R⁹ and R¹⁰ are each independently a group selected from H andsubstituted or unsubstituted methyl or ethyl, optionally wherein two ormore of R⁹ and R¹⁰ are bonded together to form a ring.
 25. Aphotovoltaic device according to any one of claims 1, 3 to 8, and 19 to24, wherein the passivating agent is a compound selected frompyrrolidine, piperidine, morpholine, 2H-pyrrole, 2-pyrroline,3-pyrroline, pyrrole and pyridine.
 26. A photovoltaic device accordingto any one of claims 1, 3 to 8, and 19 to 25, wherein the passivatingagent is pyridine.
 27. A photovoltaic device according to any of claims1 to 7, and further comprising: a further passivating agent which is afurther organic compound; wherein molecules of the further passivatingagent are disposed at grain boundaries within the metal halideperovskite and are not chemically bonded to anions or cations in themetal halide perovskite.
 28. A photovoltaic device according to claim27, wherein the molecules of the further passivating agent blockinteraction between anions and cations in the metal halide perovskite atthe grain boundaries.
 29. A photovoltaic device according to any ofclaim 27 or 28, wherein the further passivating agent comprisesnon-polar organic molecules.
 30. A photovoltaic device according to anyof claims 27 to 29, wherein the further passivating agent comprises apolycyclic aromatic hydrocarbon.
 31. A photovoltaic device according toclaim 30, wherein the further passivating agent comprises any ofnapthalene, anthracene, phenanthrene, pyrene, and fluoranthene
 32. Aphotovoltaic device comprising a semiconductor, which semiconductorcomprises: (a) a metal halide perovskite; and (b) a passivating agentwhich is an organic compound; wherein molecules of the passivating agentare disposed at grain boundaries within the metal halide perovskite andare not chemically bonded to anions or cations in the metal halideperovskite.
 33. A photovoltaic device according to claim 32, wherein themolecules of the passivating agent block interaction between anions andcations in the metal halide perovskite at the grain boundaries.
 34. Aphotovoltaic device according to any of claim 32 or 33, wherein thepassivating agent comprises non-polar organic molecules.
 35. Aphotovoltaic device according to any of claims 32 to 34, wherein thepassivating agent comprises a polycyclic aromatic hydrocarbon.
 36. Aphotovoltaic device according to claim 35, wherein the passivating agentcomprises any of napthalene, anthracene, phenanthrene, pyrene, andfluoranthene.
 37. A photovoltaic device according to any one of thepreceding claims wherein the metal halide perovskite is a perovskite ofthe formula (I):[A][B][X]₃  (I) wherein: [A] is at least one organic cation; [B] is atleast one metal cation, wherein [B] comprises at least one of Ca²⁺,Sr²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Fe²⁺, Co²⁺, Pd²⁺, Ge²⁺, Sn²⁺, Pb²⁺, Yb²⁺and Eu²⁺; and [X] is at least one halide anion.
 38. A photovoltaicdevice according to claim 37, wherein [B] comprises at least one ofSn²⁺, Pb²⁺, Cu²⁺, Ge²⁺ and Ni²⁺.
 39. A photovoltaic device according toany one of the preceding claims, wherein the metal halide perovskite hasa band gap of less than or equal to 3.0 eV.
 40. A photovoltaic deviceaccording to any one of the preceding claims, wherein the metal halideperovskite has a band gap of less than or equal to 2.0 eV.
 41. Aphotovoltaic device comprising a semiconductor, which semiconductorcomprises: (a) a metal halide perovskite; and (b) a passivating agentwhich is (i) a halogen bond donor compound, or (ii) an organic compoundcomprising at least one thiol or sulfide group.
 42. A photovoltaicdevice comprising a semiconductor, which semiconductor comprises: (a) ametal halide perovskite; and (b) a passivating agent which is an organiccompound comprising at least one heteroatom selected from N and P.
 43. Aphotovoltaic device according to claim 41 or 42, wherein the passivatingagent is as defined in any one of claims 2 to 26, and/or wherein themetal halide perovskite is as defined in any one of claims 37 to
 40. 44.A photovoltaic device comprising a semiconductor, which semiconductorcomprises: (a) a metal halide perovskite; and (b) a passivating agentwhich is an organic compound comprising non-polar organic molecules. 45.A photovoltaic device according to claim 44, wherein the passivatingagent is as defined in any one of claim 35 or 36, and/or wherein themetal halide perovskite is as defined in any one of claims 37 to
 40. 46.A photovoltaic device according to any one of the preceding claims,wherein the photovoltaic device comprises a layer of said semiconductor.47. A photovoltaic device according to claim 46, wherein the layer ofthe semiconductor is without open porosity.
 48. A photovoltaic deviceaccording to claim 46 or 47 wherein the layer of the semiconductor has athickness of at least 100 nm.
 49. A photovoltaic device according to anyone of the claims 46 to 28, wherein the photovoltaic device comprises(a) an n-type region comprising at least one n-type layer; (b) a p-typeregion comprising at least one p-type layer; and, disposed between then-type region and the p-type region: (c) the layer of the semiconductor.50. A photovoltaic device according to any one of the preceding claims,wherein the photovoltaic device is a photodiode, a solar cell, aphotodetector, or a photosensor.
 51. A process for producing aphotovoltaic device comprising a semiconductor, which semiconductorcomprises: (a) a metal halide perovskite; and (b) a passivating agentwhich is an organic compound; wherein molecules of the passivating agentare chemically bonded to anions or cations in the metal halideperovskite, wherein the process comprises treating a metal halideperovskite with a passivating agent, which passivating agent is anorganic compound suitable for chemically bonding to anions or cations inthe metal halide perovskite.
 52. A process according to claim 51,wherein the passivating agent is as defined in any one of claims 2 to26, and/or wherein the metal halide perovskite is as defined in any oneof claims 37 to 40, and/or wherein the photovoltaic device is as definedin any one of claims 46 to
 50. 53. A process according to claim 51 or52, wherein treating the metal halide perovskite with a passivatingagent comprises disposing on a surface of the metal halide perovskite atleast one composition comprising the passivating agent.
 54. A processaccording to any one of claims 51 to 53, wherein the process comprises:(a) providing a substrate having a layer comprising the metal halideperovskite disposed thereon; and (b) treating the layer comprising themetal halide perovskite with the passivating agent.
 55. A processaccording to claim 54, wherein the substrate having a layer comprisingthe metal halide perovskite disposed thereon comprises a first electrodematerial and at least one first region selected from an n-type region, ap-type region or an intrinsic region.
 56. A process according to claim54 or 55, wherein the substrate having a layer comprising the metalhalide perovskite disposed thereon comprises a porous layer of ascaffold material, wherein the porous layer of a scaffold materialcomprises an n-type material or a dielectric material.
 57. A processaccording to any one of claims 54 to 56 which further comprisesdisposing on the layer comprising the metal halide perovskite: (c) atleast one second region selected from an n-type region, a p-type regionor an intrinsic region; and/or (d) a layer of a second electrodematerial.
 58. A process according to claim 51 or 52, wherein treatingthe metal halide perovskite with a passivating agent comprises addingthe passivating agent to a solution of the metal halide perovskitebefore formation of the metal halide perovskite solid.
 59. A processaccording to claim 58, wherein the process comprises: (i) disposing aprecursor solution on a substrate, which precursor solution comprisessaid metal halide perovskite and the passivating agent dissolved in asolvent; and (ii) removing the solvent to produce a solid layer of thepassivated metal halide perovskite.
 60. A process for producing aphotovoltaic device comprising a semiconductor, which semiconductorcomprises: (a) a metal halide perovskite; and (b) a passivating agentwhich is an organic compound; wherein molecules of the passivating agentare disposed at grain boundaries within the metal halide perovskite andare not chemically bonded to anions or cations in the metal halideperovskite; wherein the process comprises treating a metal halideperovskite with a passivating agent, which passivating agent is anorganic compound that does not chemically bond to anions or cations inthe metal halide perovskite.
 61. A process according to claim 60,wherein the passivating agent is as defined in any one of claim 35 or36, and/or wherein the metal halide perovskite is as defined in any oneof claims 37 to
 40. 62. A process according to claim 60 or 61, whereintreating the metal halide perovskite with a passivating agent comprisesdisposing on a surface of the metal halide perovskite at least onecomposition comprising the passivating agent.
 63. A process according toany one of claims 60 to 62, wherein the process comprises: (a) providinga substrate having a layer comprising the metal halide perovskitedisposed thereon; and (b) treating the layer comprising the metal halideperovskite with the passivating agent.
 64. A process according to claim63, wherein the substrate having a layer comprising the metal halideperovskite disposed thereon comprises a first electrode material and atleast one first region selected from an n-type region, a p-type regionor an intrinsic region.
 65. A process according to claim 63 or 64,wherein the substrate having a layer comprising the metal halideperovskite disposed thereon comprises a porous layer of a scaffoldmaterial, wherein the porous layer of a scaffold material comprises ann-type material or a dielectric material.
 66. A process according to anyone of claims 63 to 65 which further comprises disposing on the layercomprising the metal halide perovskite: (c) at least one second regionselected from an n-type region, a p-type region or an intrinsic region;and/or (d) a layer of a second electrode material.
 67. A processaccording to claim 60 or 61, wherein treating the metal halideperovskite with a passivating agent comprises adding the passivatingagent to a solution of the metal halide perovskite before formation ofthe metal halide perovskite solid.
 68. A process according to claim 67,wherein the process comprises: (i) disposing a precursor solution on asubstrate, which precursor solution comprises said metal halideperovskite and the passivating agent dissolved in a solvent; and (ii)removing the solvent to produce a solid layer of the passivated metalhalide perovskite.
 69. A process according to any one of claims 51 to68, wherein the photovoltaic device is a photodiode, a solar cell, aphotodetector, or a photosensor.
 70. A photovoltaic device obtainable bya process as defined in any one of claims 51 to 69.